Mysterious Past

"Louis: Did you abscond with the church funds? Run off with a senator's wife? I like to think you killed a man; it's the romantic in me.

Rick: A little bit of all three."

- Casablanca

"You are being deliberately obscure as a substitute for having a personality."

- Bonnie McFarlane, Red Dead Redemption

A character has a mysterious past which is hinted at but never fully revealed.

This trope provides the writers with enormous freedom to have previously unknown (to the viewer and possibly also the character) relationships to other characters, special skills, prior histories with the Big Bad, knowledge of prophecies or the future itself, a MacGuffin, or other examples of Ass Pull as needed. In effect, since nothing is known, anything can be true.

A character can have a partially mysterious past as well; for instance, Character A was Character B's childhood friend, but when they meet up A has KGB agents on their tail and the ability to fire guitars from their eyes.

The ability to fill it in as needed is, however, limited to such elements as can reasonably be fit into the time period. A thirty-five-year-old can't have sixty years' past. Failure to submit to this limit results in an Expansion Pack Past.

Often a Former Teen Rebel's old rebellion will be part of their mysterious past. Any dark deeds done in this period are part of a Dark and Troubled Past.

Anime and Manga

 * In Noir, Kirika defines the trope nicely, although Mirielle has elements of her own past mysterious to her as well; although hers are more or less revealed in time, Kirika's past is basically left unexplained save for fragments.
 * Vash, from Trigun, has this for most of the anime and around a third of the manga.
 * Nabeshin, the Marty Stu-esque Director Avatar of Excel Saga, is revealed to share a Mysterious Past with almost all of the one-shot supporting characters, who upon reuniting with him often refer to some unspecified nebulous event that happened "that one time in Bogota".
 * A lot of people in Excel Saga have pasts that are not elaborated on. According to Dr. Kabapu Il Palazzo and him are the sole survivors of a lost civilization, but nothing has ever been explained in detail. Hyatt and Elgala might have had normal lives before joining ACROSS, but the only thing mentioned about their lives is that Hyatt joined ACROSS after seeing an ad in a newspaper, and Elgala worked at a hotel before joining ACROSS. The title character Excel might have been a completely different person before meeting Il Palazzo, based on her personality when she was amnesiac. And nothing has been revealed about Kabapu's secretary Ms. Momochi, even though she is always seen with Kabapu and interacts regularly with the rest of the cast.
 * In Gundam 00, Tieria's past and origins were not shown nor written unlike the Dark And Troubled Pasts of the other three  meisters.
 * In the earlier days of the Tsubasa fandom, Fay's past was one of the things in the series most often speculated on by Fan Fiction writers. Everybody knew something bad had to have happened, for him to be the way he was, but nobody knew what. CLAMP held out on it for about twenty volumes, and of course when it finally did come out it was worse than anyone had imagined.
 * Played with in regards to the main character Syaoran, who at first appears to have nothing to hide, but as the series goes on, hints are dropped that not all is as it seems with his history (namely, he was apparently found on the streets, at a young age, by his foster father, and has no memory prior to that).
 * Cowboy Bebop, very deftly, with the entire Five Man Band. Jet is fairly straightforward but still doesn't reveal everything. Faye . All we know about Ein is that he's a "data dog" (and we never learn what that is), and Spike and Ed we are told frustratingly nothing about, even though we meet Ed's father and Spike's past is the Myth Arc of the show!
 * , from Mahou Sensei Negima. Throughout the series clues and facts are dropped like breadcrumbs, each one redefining her as a character and the entire manga's story as a whole, but even now, with a very, very general outline, we're still mostly in the dark about it. Whatever it was, it was bad enough that she needed to erase all memory of it before she could be normal, and those memories are so dark that their unlocking created a Split Personality... and left her comatose for a week.
 * Agito of Magical Girl Lyrical Nanoha, a Unison Device from Ancient Belka who had been smacked with a case of amnesia. What little she does remember has fueled a good amount of fan discussion, especially after the Sound Stage that featured her story dropped not so subtle hints that Signum was her original master, implying that the Wolkenritter themselves are not just ordinary living programs but have a Mysterious Past of heir own.
 * Amatsuki utilises this in magnificent fashion as part of its Jigsaw Puzzle Plot, and the more that is actually revealed about past events, the more confusing things become. What happened to Toki's dead childhood mentor? What connection does Chitose have to them and to the science project that may/may not be responsible for time travel? What caused Lily's brain damage and the fire that killed her mother? What is Susutake's connection to the demons? Why did Sensai Midori disappear? Why did Kanzou split from Kuchiha? How does Bonten know the man with the IV drip? Who did Tsuyukusa kill and why was he separated from his tree? Who was Utsubushi originally? What made Yakou kidnap humans and trap them in the past? And what the hell has Kon got to do with all of this? Since when was he a hacker? Does he even have a family?
 * Interestingly while the two characters from the modern world (Toki and Kon) have very mysterious pasts, most minor characters have been explained.

Comic Books

 * The Marvel Universe has Wolverine, aka Logan, aka James Howlett (thanks to suddenly regained memories, according to recent writers). Rogue also qualified as having something of a Mysterious Past until her background and given name were finally revealed, rather anti-climactically, in her now-cancelled ongoing series, more than twenty years of realtime after her debut.
 * Ramona Flowers from Scott Pilgrim is often very reluctant to share facts of her past with even her boyfriend. The little we do learn is through rumour and so very suspect. Author of the series Bryan Lee O'Malley gave Mary Elizabeth Winstead (who played Ramona in the film), along with some of the other actors, a sheet listing 10 facts of Ramona's past, but even he said that these need not necessarily be true.
 * Indigo-1 from the Green Lantern series. Apparently Abin Sur had left a big impression on her and her tribe, but all we've known about her past so far is that.

Film

 * This trope was gleefully subverted in the Grindhouse film Planet Terror. Bad Ass El Wray's Mysterious Past is ultimately revealed, earning him the instant respect and trust of the formerly suspicious Sheriff. Unfortunately, this revelation is made in the never-actually-filmed 'missing reel'.
 * Rick Blaine in Casablanca. For all that is revealed, we still don't know why (and exactly when) he left America or why he can't return.
 * Rick's past was such a mystery, even the writers didn't know. They spent a lot of time trying to come up with something appropriately cool; they failed. One finally suggested 'unpaid parking tickets.' That was the point when they gave up and left it vague.
 * Parodied with Chance the Gardener in Being There. In the novel, it's explained that he was the offspring of a mentally damaged woman who suffered Death By Childbirth. It is strongly suggested that the wealthy "Old Man" who raised him and told him this is the father, a possibility also raised in the film adaptation though the mother's backstory is not brought up. In any case, Chance is not allowed to leave the house (in the book, he was told that he would wind up institutionalized if he did) and only does so when forced out by the Old Man's death. When the FBI and CIA investigate "Chauncey Gardiner", as the world accidentally comes to know him, no trace of him can be found (birth certificate, driver's license, etc. - all of which Chance likely never had anyway), leaving his past completely mysterious to all but a few.
 * Both great masters of the Force from Star Wars, Yoda and Sidious are given little background on their origins. (In fact, technically speaking nothing is revealed in the film continuity about Sidious's origins other than him being Palpatine: what little is commonly "known" is in fact only implied by the film and never confirmed.) Indeed, it' believed that there's a ban on Expanded Universe authors detailing either's backstory (a novel about Sidious's Master, Darth Plagueis, was cancelled for this reason).
 * Ted from Burn After Reading is shown to have once been a European Orthodox priest, before getting the job as the manager of... "Hardbodies". How does this happen and why? We may never know.

Literature
"The instructor was somebody named Whitlaw. Nobody knew much about him. It was his first semester here. We'd heard some rumors though - that he'd once punched a kid for mouthing off and broken his jaw. That he couldn't be fired. That he'd seen active duty in Pakistan, and still had the ears of the men and women he'd killed. That he was still involved in some super-secret operation and this teaching job was just a cover. And so on.
 * The Bourne books/movies almost entirely sustain off this. Though they do eventually explain...
 * Sherlock Holmes at least partially fits this trope, given that Watson comments more than once in the stories about how he knows virtually nothing of Holmes's past. All that is eventually revealed is that he's distantly related to a bunch of French painters, he attended university somewhere, he's descended from country squires, and he has an older brother who's even cleverer than he is.
 * The titular assassin in The Day of the Jackal. Although referred to throughout the book as "the Englishman" and eventually assumed to be former arms dealer Charles Calthrop, we eventually discover Calthrop is a completely different person and we've no way of knowing if the Jackal was even English.
 * Amusingly lampshaded in The War Against the Chtorr novel "A Matter for Men" by David Gerrold, when the protagonist first meets his Global Ethics teacher.

The first time I saw him, I believed it all."

"A lot of people ... still believed that, and they blamed him on every denomination from Anglicans to Zen Buddhists, not even missing the Satanists, and there were all sorts of theories about what he'd done to get excommunicated, the mildest of which was that somewhere there was a cathedral standing unfinished because he'd hypered out with the building fund."
 * "Bish" Ware, the town drunk in H Beam Piper's Four-Day Planet. It's short for "bishop," because people think he looks like the stereotype..

"Nidbjorg: "What did you do different, Thorvor? He's not the same colour. This time he's grey."
 * Very little is known about the past of Ciaphas Cain before he began attending the Schola Progenium. He claims to be from a hive world, that his parents served in a Guard regiment before being killed in a battle against some kroot, and that his great-grandfather hunted bounties (and sometimes had bounties on his own head). However, Amberley, his sometimes lover and posthumous editor, has noted that there is absolutely no documentation substantiating any of that, that some of the events described are implausible when not impossible, and that Cain tended to edit his background story to appeal to his target audience on the rare occasions that he talked about it at all. The only part of that list of facts that is likely to be true is the bit about being a hive worlder, and even then, Amberley never figured out Cain's exact world of origin.
 * Harry Dresden, of the Dresden Files, has shades of this, mostly tied up in who his mother was. Applies somewhat to his own past as well.
 * Tavi of Calderon. Why is he the only Aleran who can't furycraft? Who was his dad? Why is he a genius in a world of magical thugs and monsters? Protip: when a boy from the woods saves the day in the first book of a Fantasy series, he tends to be more than he appears.
 * In Edgar Rice Burroughs's The Monster Men, Bulan's past to Virginia.
 * Rock, Midnight and Sol from Warrior Cats. Sol's past was revealed in an Expanded Universe manga, but there are hints that he's lying through his teeth.
 * In Devon Monk's Allie Beckstrom novel Magic to the Bone, Zayvion reveals very little of his. It's one reason why Allie suspects him untrustworthy.
 * In The Elves and the Otterskin by Elizabeth H. Boyer, there's Eilifer. Ivarr is forced to help a group of outcast elves. The elves are supposed to be incompetent both as warriors and mages but gradually develop competency as the story develops. However, it's very strongly hinted that Eilifer's been lying about his competence level from the beginning and is, in fact, both extremely powerful and extremely reluctant to use his power. Why, is never revealed leaving Eilifer an unsolved mystery even at the end of the story. Lampshaded by several characters throughout the story, including a hint that this alleged outcast is connected to the elven king himself when he ambushes three evil witches by letting them turn him into a horse for hag-riding rather than their usual Designated Victim.

Thorvor: "Grey! Elbegast's horses are grey!""

Live Action TV
"Shepherd Book: I wasn't born a shepherd, Mal.
 * The title character of Remington Steele.
 * Guinan from Star Trek the Next Generation.
 * Guinan's past was partially explained in Star Trek Generations, where she was revealed as an El-Aurian refugee.
 * How the heck she ran into Q? Still not explained. Also, if there had been a fifth season of Enterprise they would have had a episode featuring Guinan during that era. Whether this would add to or remove some of the mysteriousness will never be known.
 * That's nothing. Who HASN'T run into Q at some point in Star Trek? Even worst when you count the Expanded Universe where Q is probably the alien appearing in the most books after Spock. Meeting Q is the norm, not the exception.
 * Also, what the hell was she doing on Earth
 * As the former page quote suggests, "plain, simple Garak" of Star Trek Deep Space Nine may be a tailor, but he's a tailor with several interesting stories about his past... some of which might actually have some grain of truth to them.
 * The Doctor from Doctor Who initially had a completely unknown past. By the time of the seventh Doctor, much about his past had been explained, so the writers attempted to restore the mystery by implying that much of what we had been told was a lie, and that he actually had a much darker past than had previously been suggested. Sadly, the series was cancelled before the so-called "Cartmel Masterplan" could be put into effect, and the revival hasn't returned to the idea.
 * However, in the revival, much of what happened during the Time War (which happened inbetween the original series and the new one) is mysterious.
 * Captain Jack Harkness has a lot, with both his time before he met the Doctor and between The Parting of the Ways and Everything Changes being mysterious. The series specializes in revealing dark aspects of his past.
 * Shepherd Book from Firefly, who seems to have extensive government connections, intimate knowledge of criminal culture, and can identify the exact model of a particular rifle just by looking at the bullet wounds it leaves behind, despite being "just a simple preacher."

Mal: You have to tell me about that sometime.

Shepherd Book: No, I don't."

"G'kar: Let me pass on to you the one thing I've learned about this place. No one here is exactly what he appears. Not Mollari, not Delenn, not Sinclair, and not me."
 * Every major character in Babylon 5 had a Mysterious Past, or acquired one during the course of the show. All of them.


 * Eliot Spencer from Leverage. We sometimes get hints about his past (flashback: Where's the monkey?!) but rarely any details, which is used mostly for comedic purposes.
 * Jefferson in Married With Children, although this was done for comedic effect.
 * The major characters in Lost.
 * The flashbacks of the most mysterious character, Locke, managed to erode almost all the mystery in his past, and add in some time in a commune never mentioned before or since. So what did the producers do? Skip ahead a few years in flashforward...and give him a new one.
 * You could also add in the island itself, given all the airplane crashes, ship moorings, secret buildings and structures, healing properties, etc.
 * Angel's mysterious past proved fodder for multiple flashback scenes in both BtVS and Angel. Ultimately, almost all of his past is explained and shown on-screen, so by about the end of season 4 he no longer has a Mysterious Past--he has a Very Dark Past that is no longer mysterious.
 * Mephisto in Double the Fist. What we do know is that there was a time when he wasn't batshit insane, he used to be a security guard, and is on the run for tax evasion. One episode has us meet his friend from his time in training, who is excited to see his good friend again. Mephisto proceeds to use his face as a mask.
 * The title character of House, M.D. Why is he such a jerk?
 * For the first season, House's employees and fans alike just wanted to know what happened to his leg. That was revealed in Three Stories, as House told said stories about 3 patients, each with a leg problem, to a group of med students. One of the patients was him, which Foreman caught on to, revealing it to us.
 * And as to why he is a jerk... After mumbling around the whos, wheres and whys, House may have revealed in One Day, One Room that
 * Thirteen's character is based all around this. But as she's also a Creators Pet, most people don't care.
 * We don't know anything about Cuddy's past
 * Toby Logan in the Canadian show The Listener has one of these.
 * In practically every other episode of Mutant X, someone from one of the main characters' Mysterious Past would turn up. How many ex-lovers does the typical young mutant-on-the-go have, anyway? Or never-before-mentioned siblings or parents?
 * NCIS Los Angeles: G. Callen. So flippin' mysterious even he doesn't know it. What does the "G" stand for? Even he doesn't know.
 * Which leads to a major plot hole. What government agency would give a clearance to someone whose background is completely unknown?
 * Bon Chance Louie, of the regrettably short lived Tales of the Gold Monkey, played with this by dropping improbable hints about his own unknown past.
 * Higgins, the Battle Butler of Magnum PI, clearly had a complex as well as mysterious past. And his present was none too clear either, WAS he the real Robin Masters?
 * Highlander the Series: One word: Methos. With a 5000 year backstory, we may never learn all of his secrets.
 * Played for Laughs with Adam Klaus, the suave American magician in Jonathan Creek. In "The Problem At Gallows Gate" he turns out to have a Scottish sister who calls him Chester, and no-one comments on this.
 * Many of Moya's passengers in Farscape have mysterious pasts until they get their day in the limelight and things are revealed, though some of them remained mysterious throughout the series.
 * Goofy coroner Woody in Psych appears to have a mysterious past. When being filmed for a documentary, he asked a few oddly specific questions about which countries the film might be seen in, and then spends the rest of the episode trying to disguise his voice and/or face.
 * During the first season of Mad Men, Don Draper became an instant poster boy for this trope. Although most of his mysterious past got revealed over the next season or two, it's continued to have significant repercussions throughout the series.

Tabletop Games

 * In Warhammer 40,000, the enigmatic Dark Angels chapter of Space Marines deliberately keeps an in-universe Mysterious Past to prevent the Inquisition looking too closely at them. With very good reason.

Video Games

 * Zero from Mega Man X. No one knows about his past at all, except.
 * Sylux from Metroid Prime Hunters. Nothing is known about it except that it hates the Galactic Federation and Samus for helping them.
 * From F Zero, Captain Falcon qualifies. Besides allegedly coming from Port Town, literally nothing is known about him, be it his origins or motivation. We don't even know who built the Blue Falcon (although it is hinted that he built it himself).
 * As part of his Divergent Character Evolution, Luigi has picked up a mysterious past and some dark powers that show up from time to time.
 * The Nameless One from Planescape Torment, very much so. He starts out with complete amnesia and even after he finds out the overall story of his former lives, much is still left vague.
 * Justified in Sonny, where the titular protagonist remembers nothing about his life; he can't even remember his own name, leading him to take the moniker "Sonny" after the guy who finds him addresses him as such (Sonny's dead before the first game even starts and resurrected as a zombie aboard a research vessel). In fact, the only major character who seems to have any real semblance of a canon backstory as of the end of the second game is Roald.
 * In Fallout New Vegas, the Player Character himself/herself (called the Courier) has one. You find out more about the past of your companions than anything about your own.
 * Arcade Gannon's past remains largely a mystery until the Courier earns his trust.
 * Lonesome Road, the final story-based DLC, reveals some of the Courier's past before the events of the main game.
 * In the Rune Factory series of games, the protagonist is always one of these, due to Laser Guided Amnesia where he forgets his past. One of the characters lampshades this in Rune Factory 3.
 * The Stranger in the Terminal Reality game Nocturne. Several characters make passing reference to it. A sequel is not out of the question.

Web Comics

 * Jorge, an outfielder for The Portland Wheatshippers from The Dugs- Baseball Comics has a mysterious past speckled with action sequences and general gratuitous violence. Another example can be found here.
 * When it began, pretty much all the characters in El Goonish Shive had mysterious pasts. While most of them have been answered, aside from a few events, the character with the still most mysterious past is arguably Tedd.
 * Besides his Mom and all the alternate dimension versions of him, there's this girl in the last panel who is almost identical to Tedd's female form.
 * Jonas Faulkner in The Phoenix Requiem.
 * Haley in Order of the Stick has a mysterious past. It may be revealed by the end of the strip, though.
 * Slightly Damned loves this trope, as characters and their pasts are revealed more or less on a need to know basis. It seems like quite a lot of things were already happening before Rhea ended up in hell...
 * Rin Satsuki of Touhou Nekokayou, who was Dummied Out of the Touhou game where she was supposed to make her debut. In this comic, she appears to have some sort of past in which she had a conflict with Yukari; the mystery is maintained through carefully not using As You Know. Word of God has stated that all would be eventually revealed in an associated Fanfic.
 * Bun-bun from Sluggy Freelance. At first he just came from a pet store as a joke and it was more that he had no past at all. Then the readers were finally shown some of it and the rest became very mysterious.
 * Oasis is similar, although by now we know so many details that what's missing is mainly the question of what the heck is she?
 * Almost all the characters from Collar 6 had this to an extent, with the author using how little we know about them to create suspicion of a traitor (and some real Epileptic Trees). It's now being played dead-straight with  who, as it turns out
 * John from Out There.
 * Fuzzy from Sam and Fuzzy. Recent arcs have shed light on his activities between his latest bout of Laser Guided Amnesia and until he met Sam, but what went on before that is unknown.
 * In Impure Blood, Caspian, Elnor, and Dara all have this. Bits and pieces are emerging.
 * Whatever things Caspian's father covered up.
 * Why Elnore got attached to Dara, and why either of them stick around Caspian when they could individually beat him to a pulp.

Web Original

 * Smith from Critical Hit has this problem. Neither Rob, his player, nor Rodrigo, the GM, have revealed how much he knows himself, or what exactly is the cause of this.

Western Animation

 * Gadget from Chip 'n Dale Rescue Rangers has got a very Mysterious Past with only a couple of hints given in one episode. Her past is frequently Ret-Conned by Fanfic authors with many different outcomes.
 * Most of the hints are in the pilot episode.
 * Galaxy Rangers: Robert Mandell and crew explored three of the Rangers' pasts with "Ariel" and duologies "Phoenix / New Frontier" and "Supertroopers / Galaxy Stranger." The show was canned before exploring Doc's backstory, leaving only a few hints that, given Doc's fast-talk ability, may or may not be the whole truth...
 * The titular character of Jimmy Two-Shoes. There have been several references to the fact that he's an outsider, but exactly what he's doing in Miseryville has not been revealed.

Real Life

 * Tommy Wiseau's past is virtually unknown. He claims to be from America, but his accent suggests otherwise.