Who Is This Guy Again?

exenefevex: Now according to the nice people on the internet... World 6, will feature Morton, who is not Roy.
exenefevex's Dad: Oh, but Morton is not Roy?
exenefevex: Yes. Do we ever fight the Morton who is Roy? There's no such thing. But that is, in fact, Morton, and not Roy.

—Let's Fail New Super Mario Bros. Wii, long after misidentifying Roy Koopa as Morton Koopa Jr. earlier in their playthrough

The fearsome recurring villain has struck again! The heroes grit their teeth and draw their weapons, prepared for the fight of their lives. They've spent most of the arc waiting for this battle. It's time to bring down... umm...

Who Is This Guy Again?

Sometimes a series just has a hard time giving you the names of its characters. People are referred to in a manner that makes it hard to work out their actual names. Sometimes it's because everyone is past the first-name basis ("Hey, man, how're you?"); by contrast, it might be because there's a more strict social structure, and people are throwing orders around ("You! Get Me Coffee!" "Yes sir!").

Either way, nobody ever stops to introduce themselves, and nobody ever introduces anybody else, to the point you're studying the end credits just to work out what these people are called. This has the benefit of being slightly more realistic, as people generally don't go around name-dropping everyone they talk to. However, Realistic Diction Is Unrealistic—it's generally an accepted element of fiction that at least the early appearances of a character will give us a name to attach to a face.

If a series takes too long to tell you a character's name, expect the Fan Nicknames to flow.

This is different from No Name Given or Everyone Calls Him "Barkeep" in that Who Is This Guy Again? characters actually have names. They're just hard to work out. More embarrassing than Expecting Someone Taller. If you know all the names but still have trouble telling people apart, they may have Only Six Faces. Those Two Guys are when they have nothing to do with the plot besides being background and providing some mundane exposition.

Contrast with Intro Dump. The inversion is Remember the New Guy?, where a new character is introduced that has never appeared or been mentioned before, but the cast are long familiar with to the point where the audience should have already met them.

Examples of Who Is This Guy Again? include:

Anime and Manga

Martian Successor Nadesico is a major offender in this regard. For example, there are three Bridge Bunnies. Megumi is part of the Love Dodecahedron, so her name comes up a lot. Ruri is quite distinctive. But name the third. Minato. While you're at it, name the guy with the bowl cut who joins the crew along with Akatsuki and Erina. Admiral Munetake. Or the head chef Ms. Howmei. The characters in the Show Within a Show, Gekiganger 3, are easier to identify by name than the cast of this show.
- Minato has a romantic subplot that is an important part of the second half of the series, at least. Before that, there's Two Big Reasons that make her memorable...
Tengen Toppa Gurren Lagann is rather stingy when it comes to even often-seen members of the Team Dai-Gurren. Name four of them, not counting Kamina, Simon, Yoko, Nia, Leeron, Rossiu, Kittan and his sisters, Viral, or Lord Genome. Hard, isn't it? Of all of the other characters, five are namedropped exactly twice in the first two arcs, one takes fifteen episodes to get a name, and the rest have their names mentioned once and then left unsaid
- How bad is it for these characters, you ask? The page linked to above has been deleted from Wikia.
The Mechanic Couple in Godannar, while being the cutest couple in the show, if they did get names, they're used once.
- Nanae Hayashi is rather important to the resolution of the final crisis. And... okay, Morimoto might not even have a given name.
In Saint Luminous Mission High School, most of the characters aren't addressed by name until the episode focusing on them.
Canada in Axis Powers Hetalia. In fact, he's the definition of this trope.
- Who?
Poor Kunikida is so unknown that he hadn't even been mentioned yet. The novels make it a bit easier for him, since his name is mentioned whenever he appears (obviously), but not by much.
Happens in Fullmetal Alchemist with Yoki (even in-universe), and it's justified—he debuts as a Harmless Villain in the manga's third chapter, and this was one of the two stories skipped in Brotherhood (though they do set that Chekhov's Gun early in episode 4, new viewers were likely left in the dust).
The French Macekre of Dragon Ball went through this phase on the Saiyan and Namek arcs, as villains, even Vegeta and Freeza, respective Big Bads of each arc, would be called almost always the rather generic term "the enemy", confusing the hell out of viewers. Some villains, such as Zarbon, were lucky to have their name said on dialogue once or twice, but never on recaps. At one random episode, they started giving people names again.
Genzo in Oh! Edo Rocket. Funny enough, he shares the same seiyuu as Canada.
Helmeppo from One Piece is the butt of this several times. Despite being one of the series' first villains, neither Luffy nor Zoro remember him or his name when he and Coby see them again in Water 7, much to his comedic chagrin.
Kamichama Karin: Kirio fails to give his name the first time he shows up, which leads to Karin calling him "Mr. Glasses Man" for the rest of the series, due to not remembering his name.
Averted in Legend of Galactic Heroes: Whenever a character appears who has not been onscreen for a while, his/her name is shown in the subtitles. Sometimes it isn't enough.
Michiru in Nagasarete Airantou.
- At least five out of all of the inhabitants in the island remembers her existence.
  - Justified, since she's always in her house.
In Yu-Gi-Oh!: The Abridged Series, Bakura is this, many of the characters not recognizing him recognizing him, even though he goes to school with the protagonists and plays a significant role in the entire series.

Tristan: Hey look, it's some random stranger we've never met before!
Joey: 'Scuse me pal, but have you seen any minor characters from season 1 around here?
Bakura: Actually, guys, I was a minor character from season 1! Remember?
Joey: Sorry pal, doesn't ring a bell.

Comic Books

One of the things The X-Axis criticised Nick Fury's Howling Commandos for:

After reading it through once, I realised that I couldn't remember the names of any of the lead characters. So I read through it again, and this time I took notes. Even then, I could only identify the names of three of the lead characters. I then crossreferenced with the Howling Commandos' entry in this week's Official Handbook, whereupon I discovered that (a) one word which seemed to be a name from the context wasn't one at all, and (b) four of the lead characters aren't named anywhere in the comic.

In 52, Bea plays a very important (if minor) role within the series. She consoles Ralph Dibny, confronts Booster Gold, and serves as the heart of the hero community, all while only speaking on the phone and later appearing "on-panel" for two small scenes. Unfortunately, she is only ever addressed as "Bea," and is never called by her superhero name, last name, or shown in her costume. The series does not make it easy to identify which character she is in the DC Universe.
In the first arc of the 2010 relaunch of Birds of Prey, the Birds wind up fighting a mysterious Asian woman dressed all in white who identifies herself as the White Canary. The team has absolutely no idea who she is and theorize that she might be either Cassandra Cain or Lady Shiva, two candidates that do not soothe their thoughts. Ultimately, it is revealed that she is the sister of the Twelve Brothers in Silk, a Reveal that came at the end of five issues and after numerous "Who is she?" questions, except the Twelve Brothers in Silk themselves have not been seen, or even mentioned, in several years, appearing in only a handful of issues of BOP in a self-contained arc. There was also nothing in her appearance or fighting to serve as a hint to the reader, despite Black Canary claiming to have figured it out from body-language clues, and after her reveal there is no mention of her true identity again for the next two issues, remaining only the White Canary for the remainder of her appearance in the series. If a reader had skipped a bare two pages of Issue #4 they would never have learned her identity at all.

Film

Colonel Mertz von Quirnheim in Valkyrie - despite being a fairly important character, you only learn his name via screen caption while he's being executed.
The first film of The Mummy Trilogy doesn't seem to mention Ardeth Bay's name anywhere. His first speaking scene in the sequel comes complete with two characters greeting him by name, as if to make sure you know what it is.
The terrible lighting and sound quality of Ax 'Em makes it impossible to figure out who anyone is, which isn't helped by the fact that some major characters die offscreen and others seem to die onscreen multiple times.
Seven Samurai has had at least two sets of English subtitles; in one of them, two of the title characters are never named.
In Inglourious Basterds, some of the Basterds don't get any mention on-screen.
In Dungeons & Dragons the dwarf’s name (Elwood) is only ever mentioned in a deleted scene.
The Ewok that Leia first meets in Return of the Jedi is called "Wicket", but you only find that out in the end titles, as the Ewoks can't talk. In fact, because of their lack of speech, the word "Ewok" is never mentioned in the actual film either.
- Palpatine's name is never given in the original trilogy; he is only ever refered to as The Emperor (or variants like "Your Highness", "My master" etc.), but he is called Senator Palpatine in his first scene in The Phantom Menace, which is an Easter Egg for those fans who learnt is name from other sources and he becomes a Devil in Plain Sight for them (and those who looked at the cast credits / knew the actor, of course).
- An Urban Legend is that Boba Fett's name is never given in the original trilogy, except in the credits; it is, but it is only given briefly and you need to really pay attention- Han Solo shouts "Boba Fett! Boba Fett! Where is he?" in Return of the Jedi immediately before he accidentally kills him. Since this is an action scene and his name is never given on-screen, its unsurprising that many people didn't hear it.
- May or may not apply to any given character who appears on screen in any Star Wars movie. The lore for Star Wars is massive, which means basically everyone has a name, though it's up to the viewer whether any occasions are this trope, or if the character is simply too unimportant to the story.
Kissy Suzuki's name doesn't appear anywhere in You Only Live Twice, despite her being the Bond Girl who Bond shacks up with at the end of the movie. They even get married in her very first scene, for Pete's sake!
The main character of Battlefield Earth is referred to by name over an hour into the film. Whether this was an attempt at creating a bond with the audience or a simple oversight is anybody's guess.
The main character in Fight Club is never named through the entire movie and in the credits is only called "narrator."
The love interest in Surf Ninjas has her name mentioned only once in the movie. It's mentioned during an action sequence, in panicked dialogue, and because of the way it's said, it isn't even obvious that he's saying her name.

Literature

In The Merry Men, a famous short-story written by Robert Louis Stevenson which went on to inspire Joseph Conrad's Heart of Darkness (which in turn was adapted into Apocalypse Now), the name of the protagonist - Charles Darnaway - is only mentioned once or twice, and deep into the book. Unfortunately, this book is also frequently used in Scottish schools for English classes, which leads to many students having to search Wikipedia for the protagonist's name.
While most of these are the result of not seeing names enough, the Honor Harrington series sometimes strays into this via an overabundance of names. Each character will generally be introduced with full name, rank, and title the first time they appear (and some of these get pretty long). In later appearances, they'll be referred to interchangeably with any one of the four (First name, Last name, rank, or title, or some combination thereof), which can make a private conversation between two people seem more like a full-blown staff meeting. Combine this with having to keep track of several ships and their whole crews (on both sides), and it's easy to forget who's who. A handful of Gender Blender Nicknames, such as Honor's best friend Michelle "Mike" Henke and her fellow officer Gervais "Gwen" Neville, only add to the confusion.
Due to its having Loads and Loads of Characters, it can be hard to keep track of who each of the characters in The Silmarillion are (particularly considering that several can go unmentioned for whole chapters at a time). The worst offenders are the House of Finwë, whose members often have very similar names (there's Celegorm, Caranthir, Curufin, and Celebrimbor; Amrod, Amras, Aegnor, and Angrod; Finwë, Fingolfin, Finarfin, Finrod, and Fingon), and to a lesser extent the House of Elwë (Elwë, Elmo, Elwing, Elrond, Elros).
- It also doesn't help that lots of characters have multiple names. So Elwë, which in Sindar is Elu, not to be confused with Eru, who is aka Illuvatar, is aka Thingol, which in Quenya is Singollo, not to be confused with Sulimo, who is aka Manwë.

Live-Action TV

In The Amazing Race, teams are usually referred to by the names of both contestants. Because of this, it's easy to forget which team member is which on homogenous teams (such as the second season's Chris & Alex and Osward & Danny).
- In an attempt to make this easier on the viewers, when next to each other, such as on the mat or in post-leg interviews, teams sit or stand in the same order as their names will appear on the screen. Meaning the racer whose name is first is always on the viewer's left.
"The Engaging Chevrons Guy" from Stargate SG-1 took many seasons to be identified despite being ever-present — it's actually Chief Master Sergeant Walter Harriman). For the longest time, though, his nametag said "Davis," as did the nametags of many a random extra.)
- This is largely subverted in the later seasons, though, as he gained enough popularity to be directly addressed by his name even several times in a single episode.
Heroes: Noah Bennett, Claire 'The Cheerleader' Bennett's adoptive father, though he became a major character well into the series, was originally a menacing "government conspiracy" type figure. "HRG" was coined by Tim Kring and used in the original pilot script, so as not to give away the reveal that he's Claire's father. This eventually stuck with the fans.
- The series has a habit of being reticent with the names of the morally ambiguous Company operatives. Neither Eden McCain nor Bob Bishop is named in their first appearances and HRG didn't get a first name till the very end of season one.
  - A funny example of this trope, seeing as the past 3 years were spent hearing everyone call the Haitian... 'The Haitian.' As soon as the series names him, every character in the series starts using his real name in all references to him. More than likely, the writers just couldn't think of a name until season four.
    - Perhaps Claire (who was the first person to say his name) asked him and then shared with everyone?
      - To be fair, there have been a few time skips in-between the seasons, and several characters are related to one-another. Its not unfeasible that they learnt it off-screen.
Tom on Lost first appeared in the season 1 finale but was not named besides being credited as "Mr. Friendly"; his repeated appearances in season 2 also left him without a real name. When his name was finally revealed as Tom in the season 2 finale, some fans continued calling him Mr. Friendly, to the point that up until his death the press releases continued to call the character "Tom/Mr. Friendly" to avoid confusion. As his last name has never been revealed, some speculate his full name is "Tom Friendly," a name that was made pseudo-canon in the captions of an enhanced episode.
- Mikhail Bakunin was also not named when he first mysteriously appeared on a TV in the Pearl station; his nickname onset was "Patchy" and this was adopted by the fan community. However, his name was revealed immediately upon his second appearance, and so he didn't fall victim to the same confusion Tom did.
"Future Guy", the recurring one-man Omniscient Council of Vagueness from Star Trek: Enterprise. They never did give him a name, or even come up with one. Eventually, the Star Trek Novel Verse offered answers; see Star Trek: Department of Temporal Investigations.
The Wire, as part of its Viewers Are Geniuses/Better on DVD package, often doesn't namedrop characters on first appearance, and not very often afterwards. Add to this that actors' names in the credits aren't even linked to their character name, and that many of them go by nicknames, and things can get confusing...
The Cigarette Smoking Man from The X-Files. It makes sense that none of the characters know who (or say) this mysterious figure's name, and it's not in his interests to tell them, but it meant he was just known by Fan Nicknames, at least until Mulder referred to him as "Cancer Man".
A running gag in season 6 of Buffy the Vampire Slayer was that no one could remember Andrew's name. He was always "that other guy." His biggest claim to fame was being "Tucker's brother."
- This was actually a meta joke about how Andrew was the only member of the trio who had never appeared on the show before, so fans would likely be calling him that anyway. Originally Tucker himself was going to be in the group, but his actor wasn't available so they had to create someone new.
- He's the Big Bad of the Musical Episode, he threatens to take Dawn to the underworld and make her his queen, he has many names... But he never actually gives one. The end credits say say 'sweet demon makeup done by...' and so the fandom has adopted the name Sweet for him ever since.
The rebooted Battlestar Galactica had this problem with the Cylon clones, especially the Sixes, which frequently had, but didn't use distinct names. It was important to know which you were watching (as they were distinct characters), but there was frequently very little way to tell. Of course, the fact they all impersonate each other anyway all the time didn't help. Avoided for the most part with the Eights when Sharon Agathon took the callsign "Athena", and names didn't matter as much with the other models as they had less differentiation. And they never even named the hallucinations, which got the Fan Nicknames Head!Six and Head!Baltar.

Theater

William Shakespeare was often stingy with character names. In Hamlet, Claudius is never actually named except in the stage directions; the other characters all just refer to him as "the King". In Twelfth Night, Viola doesn't reveal her real name to the audience until the very last scene (though she has the excuse that she spends most of the play in disguise).
Also frequent in Gilbert and Sullivan; many of their operettas have a character whose name is given in the script and program, but never mentioned (or barely mentioned) onstage: Pish-Tush in The Mikado and Cousin Hebe in H.M.S. Pinafore are examples.

Video Games

Lovingly Lampshaded in Disgaea with the line: "Your new name is...Mid Boss!!"
A minor case, from Onimusha 2: There's a very awkward conversation between two previously seen members of the Quirky Miniboss Squad before the second fight with Gingamphatts. The conversation appears to be there simply to name both of them.
Played Knights of the Old Republic 2? Yes. Remember Visa's master, the awesome negative Force wedgie with the graveyard battleship? Of course. Do you remember his name? No. Because he was only named once, in cut content (Darth Nihilus). What about The Dragon, with his fractured body and ability to survive everything you could throw at him? Of course. Do you remember his name? No. Because he was only named once, by the player character before they even knew the name (Darth Sion).
- Are there any players of that game who do NOT know these names? At the very least, they show up above the person's head when you fight them.
Beauty spends so much time insulting Dandy in Ghost Trick that you only find out his name if you've read the manual.
One of the major problems EA's RPG, Lord of the Rings: The Third Age, is that the people in your "fellowship" rarely ever say each other's names. In the first with Idrial and Berethor, they're introduced properly, but in all the other cutscenes, playable characters are called by their race: Gondorian, she-elf, ranger, dwarf, human. You can find out their names if you open up the menu, but it's easier to think of them as Not-Aragorn, Not-Gimli...
This happens to Luigi constantly in the Mario & Luigi games, especially in Superstar Saga.
- This can be invoked a few times in the first Paper Mario with Jr. Troopa (and later, the Koopa Bros.). He'll ask if you remember him, and you can answer "No" to tick him off.
The Elder Scrolls: Oblivion has a few NPCs that no one seems to be able to remember the name of. For starters, what's the champion of the Imperial City Arena's name? The Grey Prince, yes, but what about his real name? It's Agronak gro-Malog, for the record. Also, Dar-Ma's mother is always called just that in the community, but never by her real name. The kicker here? Every NPC's name comes up when they're selected in-game.
In Portal 2, despite him being one of the very few characters, you only "officially" learn Wheatley's name around a third of the way through the game. Granted, this only happens if you play with subtitles off and have ignored pretty much every prior coverage of the game, but still.

Web Comics

Happened with Tycho and Gabe early on in Penny Arcade's history before they were mistaken for Author Avatars.
Darths and Droids parodies the trope in this strip. The Rant points out the inherent problem with making NPCs too memorable; your players tend to completely forget about the "ordinary" ones.
Xykon treats protagonists like this in general, particular Roy and The Order of the Stick. During their showdown at the battle of Azure City, he eventually recalls Roy from the dungeon with the first gate as "that guy! Who was angry about… something…"
- Although sometimes he can remember Roy's last name, Greenhilt, well enough to make a passing comment about "Bluepommel."
- This is at least in part due to what he does on a daily basis. When Roy tries to narrow it down for Xykon, he mentions that he killed several unrelated people with the same name in the same city. Xykon remembers well enough once he connects that particular murder to how hard it was to clean out the blood stains.
In Shortpacked there's Ken, who rarely showed up and had no importance for a long time. This was lampshaded when one of the characters asked who he was despite him working at the titular store for 6 months at that point. The next strip featured Ken actually doing something.
In the Ace Attorney fan-comic Kristoph Gavin Ace Attorney, we have, uhhh... that detective. The science guy. Simon Taylor. Yeah, him.
Scandinavia and The World has the Faroe Islands.
Any time Penny appears in Domain Tnemrot, at least one commenter will ask who she is.

Western Animation

Marceline's Dad in Adventure Time. For his first episode, after being summoned from The Nightosphere where he rules, he's referred to as either "Marceline's Dad" or "The Lord of Evil" while he's roaming the earth and sucking out people's souls. We later find out his name, Hunson Abadeer, when Finn and Jake go to the The Nightosphere in season 4.