Mook Promotion

You know this guy. You've seen him before. There are a million others like him, and they're all the same. He's just another minor pawn in the Big Bad's army. He probably doesn't even have a name. And yet...

Sometimes, a basic generic minion isn't content with remaining so. Instead, this character, initially so insignificant that you might not even think of them as a character, becomes a major antagonist. This may be achieved through actual promotion (Klingon-style or otherwise), through a transformation, or through doing something so vile that they personally become the target of the wrath of the fanbase. Alternatively, the writer may simply give the character more and more lines and appearances until they become a significant villain through sheer familiarity. In video games they may take the form of a regular enemy who functions as a level boss, making them an inversion of Degraded Boss.

After all, every villain has to start somewhere. Maybe even the Big Bad was a mook once.

Contrast Villain Decay, where a major antagonist becomes less major as a series progresses, as well as Boss in Mook Clothing, where the enemy is clearly meant to be a "basic generic minion" but is as tough as a boss. See also Not So Harmless.

See Dragon Ascendant for the next step up the career ladder. See also Mauve Shirt and Ascended Extra for a similar promotion to a member of the Redshirt Army.

May overlap with Chekhov's Gunman, since the boss looks generic at first, but if he shows up more times he becomes important.

Anime and Manga

 * Pokémon Special plays this forward and backwards in the R/S arc. For their success in stealing a vital submarine component, Archie promotes Ark, Amber, and Angie to Admin status, but they have a new mission as a price tag - they failed to bump off Chairman Stone due to the interference of one Sapphire Birch, so their new mission is to put her on ice.
 * The inversion comes after Archie takes Amber and Angie onto the submarine provided by Maxie 60% of the way through the arc - said sub required the component that was stolen earlier. Archie ordered Ark to stay put and defend the base as a means of demoting him. Prof. Starstone provided the meteorite to Angie that Amber used to kill Mt. Chimney, but Sapphire's still alive, right?
 * Then Amber gets demoted and left for dead by Archie...for doing his goddamn job perfectly.

Comics

 * In Marvel's G.I. Joe comic, the S.A.W. Viper who killed Doc and a few other Joes was just a nameless mook. At the same time, Hasbro introduced an unrelated character to the toyline named Overkill who was originally a soulless android. Later versions of Overkill retconned his background as a Cobra soldier who had half of his body parts replaced with cyborg implants. The Overkill in the Devil's Due series is a composite of the formerly nameless S.A.W. Viper from the Marvel series and the second Overkill from the toyline.
 * Remember Mr. Morden of the Brotherhood of Evil? Probably not. But after the Brotherhood disbanded, he underwent sanity experimentation and became Mr. Nobody, leader of the Brotherhood of Dada and one of the greatest enemies of the Doom Patrol.

Film

 * In The Godfather movies, Al Neri and Rocco Lampone are minor hitmen in the first movie and are promoted to bigger roles as Michael Corleone's capos in Part II. Willi Cicci is also a hitman with few lines in the Part I, then Frank Pentageli's right hand man in Part II. In Part III he was supposed to appear again in a No Celebrities Were Harmed version of real life mobster John Gotti but the actor Joe Spinell died before filming began and was replaced by Joe Mantagna playing a new character "Joey Zaza".
 * One of the more striking examples is Boba Fett from Star Wars. He started off as just a freelance version of the Faceless Goons who was hunting Han Solo. He never actually fought anyone and his death was rather mundane, his jetpack was damaged and he flew out of control into the Sarlaac's mouth. And yet He and Bounty Hunters like him are one of the most popular aspects of the Fandom.
 * The Brain Gremlin in Gremlins 2 gets, as you might suspect from his name, an intelligence upgrade and instantly becomes the creatures' leader and spokescritter.

Literature

 * In Mariel of Redwall, Terramort searats Garrtail and Grimtooth were promoted to Captains following
 * Don't forget Slagar.
 * Ripfang in Lord Brocktree. Initially a young ex-searat and recent recruit into Ungatt Trunn's horde, Ripfang's brutality and cleverness enable him to swiftly rise through the ranks, becoming one of Trunn's Co Dragons alongside Karangool and the Grand Fragorl. By the end, he's the only major villain left (and may go on to become a pirate who threatens Salamandastron on his own in Mossflower depending on who you ask).
 * Padan Fain from the Wheel of Time series. Long story short, he was the original Agent Smith.

Live Action TV

 * In Star Trek the Next Generation, a Borg drone is given the name Hugh in the episode "I, Borg". He would eventually stir up trouble by getting into a misinformed alliance with Data's Evil Twin Lore in the "Descent" two-parter (he helps the heroes later after he realises Lore's exploiting the drones.) Perhaps the ultimate example--it's harder to get much mookier than a Borg drone without getting into naturally-occurring hive minds.
 * Damar in Star Trek Deep Space Nine was first introduced as a random Cardassian bridge officer. In fact, he was always going to be a much meatier role, and was shot like a main character throughout that episode, but that didn't stop the actor nearly turning down the role because he felt it was a meaningless bit part. In fact.
 * Braca of Farscape has a very interesting career path - he starts off as seemingly just another Red Shirt, but his loyalty to Scorpius, unthreatening demeanor and ruthless opportunism means that by the end of the series, he's gone from being a random mook to having his own command (and even a first name).
 * In the final season of Smallville, Gordon Godfrey starts out as just one of Darkseid's host bodies, used by him to start an anti-hero Propaganda Machine. However, Darkseid must have liked what he saw in him, because when he's next seen, he's been promoted to Co-Dragon along with Granny Goodness and Desaad.

Tabletop Games

 * In Dungeons & Dragons, baatezu and tanar'ri (devils and demons, essentially) "evolve" from weaker forms into truly nasty monsters that are easily a Boss Battle on their own.
 * Except for erinyes, which are born as such but can still evolve higher.
 * In a 3.5 rulebook it is explained that when a Baatezu gets promoted enough it can rise to a rank of 'unique' and be given, uh, unique-ness.
 * As well, a lot of D&D rulebooks, especially 4e, have templates you can apply to bog-standard monsters to make them more challenging.
 * The Chess pawns can become more powerful pieces when the player reaches the other side of the board, making this trope Older Than Feudalism.
 * Inverted in Paranoia, in that it's the players who are the mooks of Friend Computer, promoted up out of Infrared anonymity to be Red-level Troubleshooters. In theory, they could go even higher, but seldom live long enough to do so.
 * Unusual semi real life example: Feared Warhammer 40,000 Ork Warboss Ghazghkull Mag Uruk Thraka was originally just a regular mook in the army of one of the game developers, with the name created via random generator tables. Over time he was given his own new model and rules as a Warboss, his backstory developed and was eventually resculpted as a giant tank on legs and holds the position of the most feared Greenskin leader in the universe.
 * The backstory of one supervillain NPC from the old GURPS Supers, Darkshell: he was a rather stupid thug hired to test a Powered Armor suit for a Mad Scientist. He slowly becomes smarter, and not only that - he becomes able to read minds. Thus he realises the Mad Scientist hadn't bothered to put in radiation shielding on the suit's Phlebotinum reactor, reasoning it was just a prototype and not caring if his minion died - not counting on the risk of a Freak Lab Accident. Darkshell kills him, now that he is smart enough to handle the armor himself, and sets out to become his own villain.

Video Games

 * The Man Eater, a regular enemy in Aria of Sorrow, appeared in the Boss Rush for some reason.
 * Possibly as a bane to speedrunners, annoying three-headed bastard...Well technically eyes, but you have to kill every one of them. If you're not using the Red Minotaur when you enter, you should be.
 * And by Order of Eclessia it's gotten to be a full-fledged boss at the end of the Skeleton Cave.
 * Spectral Sword first appeared in Symphony of the Night and was a normal enemy in several games. It finally got promoted to boss status in The Adventure Rebirth.
 * The King Goomba in Paper Mario, who begged king Bowser to turn him into a king using the Star Rod.
 * In Spyro the Dragon 3 the bosses are all Mooks which the Big Bad turns into monsters.
 * In Live a Live, in every room of the Technique Dungeon, you will be pursued by an obese, pink guy who seems to be infatuated with your player character, no matter what gender they are. Being caught makes a fight ensue. If you finally find the treasure of the dungeon, he will fight you again for one last time... except the only thing that changes is that the boss song plays. He's still as strong as he was before.
 * Nearly every boss and sub-boss in Yoshi's Island is a common enemy turned giant by Kamek.
 * In The Legend of Zelda: The Minish Cap, minor enemies are occasionally promoted to Giant Mook bosses. In this instance, though, the enemies haven't become more powerful; Link has simply been shrunk to a smaller size.
 * Johnny Sasaki from Metal Gear Solid. In the first game he was a bid at humanising the mooks by giving one a name and history. In Metal Gear Solid 2, he graduated to the role of recurring comic relief character. By Metal Gear Solid 4 he becomes, in a scene that really has to be seen to be believed,
 * A beefed-up Hammer Bro. in Super Princess Peach served as the precursor to the Final Battle.
 * Final Fantasy VI: sort of...
 * Ultros from the rafting level looks like a one-time boss, but just keeps inexplicably showing up.
 * In Super Robot Wars Z, an anonymous female grunt witnesses her squad wiped out by the time/space bomb at the start of Orguss. She is Xine Espio, Akasim's sidekick.
 * In City of Villains this is a major part of the plot line for the Arachnos archetype player characters.
 * In the fluff of Sword of the Stars, for the Hivers, if your mommy loves you very much, when you die, she'll eat your brain and reincarnate you in a new body, with the chance of being reborn as a Prince. And if you should manage to impress grandma enough, you might even come back as a Princess.
 * All of the Chapter 6 Guardians in Dark Cloud 2, which protect the crystals needed to activate the Time Gate, are regular enemies given a massive HP increase. Likewise, the foes that bar the way across the Spiral Of Dreams at the endgame are bigger and badder versions of already difficult mooks. Their tactics remain exactly the same, however.
 * The Kingdom Hearts series has been, as of late, giving upgrades to the Shadow Heartless, including adding supersized-versions for 358/2 Days, and creating their elite subspecies, the Neoshadows. Then, they have a promoted Neoshadow, called Novashadow, as a boss battle.
 * Patapon has an example that covers two games. In the Desert Level, when you kill Aiton, a minor Zigoton soldier, his friend Makoton swore revenge on all Patapons, even going to the point of leaving General Gong to die and selling his soul. In the sequel, he was the Dark One said to hate all Patapons.
 * The Waddle Dee in Kirby Superstar Ultra, Revenge of the King. You actually hear King DeDede promote him right before the fight.
 * Particularly notable considering that Bandana Dee, as he's more often known, has been promoted to playable in Kirbys Return to Dream Land.
 * Captains in "Rome: Total War" can be promoted to Family Members after winning battles.
 * Those two Mandibugs that are stacked on top of each other from Super Mario Galaxy and Super Mario Galaxy 2.
 * In the final area of Teenage Mutant Ninja Turtles, the recurring Laser Soldier mook gets promoted to a Mini Boss right before the final Battle with Shredder.
 * In the Modern Warfare series, Vladimir Makarov, Big Bad of the second two games, was in fact just another soldier in Zakhaev's army when Price shot his arm off in Chernobyl in 1996. Makarov saved Zakhaev's life and was rewarded as a loyal minion, rising through the ranks of the Ultranationalist command until Soap killed Zakhaev in 2011. Makarov took control of the radical elements of the Ultranationalists, and became a vastly greater threat than his mentor ever was.

Webcomics

 * Redcloak of Order of the Stick is an archetypal example. Author Rich Burlew at first intended for him to be an ordinary Mook, and indeed the name Redcloak derives from the original Star Trek's tradition of killing off its "redshirt" security officers. The character, however, took on a life of his own and became the living vessel of the will of the god of goblins. Not a bad promotion!
 * Redcloak's right-hand man may be a case of this as well. Word of God suggests that the seemingly various hobgoblins that have filled this position are in fact just one hobgoblin--Jirix--who has been resurrected behind the scenes each time.
 * The wight with Thanh's shoes was one of Tsukiko's generic wights, but he became the only one to survive the encounter and has now been seen as her Number Two ever since. He even got to hang out with Xykon.
 * This fellow in The Last Days of Foxhound tries this. It doesn't work out, since nobody remembers him.
 * Stanley the Plaid/Tool of Erfworld, the protagonist's Overlord, is revealed in his backstory to have started off as a piker - which amounts to line infantry. That's one hell of a promotion.
 * Technically, Stanley had four promotions: Piker to Warlord, Warlord to Chief Warlord, Chief Warlord to Heir Designate, and finally, Heir Designate to Overlord. And promoting common infantry to Warlords is not that uncommon in Erfworld, and is one of the two ways of becoming a Warlord in Erfworld. The other is being born popped into the position.
 * A Random Encounter in RPG! World had Olaf, who after "Disc 1" returns in Monster City as a Boss with his girlfriend still upset and traumatized that the Player Party ran away from him.
 * It might've been a tutorial how to run away from monsters though.. Fat blokes. Honest.
 * One of Dr. Nefarious's henchmen in Antihero for Hire returns in an interlude phase later on as Union, gathering mooks of all kinds, for... well... Exactly What It Says On the Tin.

Western Animation

 * Harley Quinn from Batman the Animated Series was originally supposed to be a minor accomplice of the Joker and ended up a full-blown Super Villain, making appearances in numerous other adaptations.
 * The Monarch of The Venture Brothers used to be a mere henchman for Phantom Limb before gradually building himself into Dr. Venture's archnemesis and being the Big Bad for the first two seasons.
 * Also from The Venture Brothers is Henchman 21, who, as the name indicates, was just another generic henchman until
 * In The Batman The Black Mask would kill his Number One then point to a random mook and make him or her his new Number One.
 * Shego in Kim Possible was originally designed as a fairly generic henchwoman for Dr. Drakken, but Nicole Sullivan's performance pitched her as smarter than Drakken, treating his evil schemes with mockery and sarcasm. The writers remade her to include this, and she became the series' most popular villain.

Real Life

 * Adolf Hitler: Mook in World War I, promoted to Big Bad by the time of World War II
 * Napoleon Bonaparte: Freshly minted 2nd Lieutenant to de facto ruler of France (must be said he went all the way up to general before making a coup).