Bunnie Rabbot of Archie Comics' Sonic the Hedgehog first appeared in a pin-up in the original four issue mini-series before appearing in the comic proper some issues later. She also looked markedly different.
Dr. Finitevus first appears during the "Return to Angel Island" arc as just another member of the Dark Legion. About 40 or so issues later, he joins the Big Bad Ensemble by manipulating damn near everyone in order to ensure Knuckles becomes the new Enerjak.
Dr. Finitevus had been around earlier than that - when Knuckles first started showing signs of being "Chaos Knuckles", he was the echidna who used the Chaos Siphon to try to drain Knuckles' power.
The locust swarm that causes the Bone brothers to get separated in the first issue of Bone seem like just some natural, albeit random, occurrence. After the scene where the swarm separates the Bones the locusts disappear and don't seem to have been all that important. That is until later when we learn about who the Big Bad is. He's called The Lord of Locusts.
Practically anyone who has ever appeared in the Prelude but not in the graphic novel of Dreamkeepers is suspected to be one of these.
Empowered has Ocelotina a female hostage Emp tries (and fails) to save from ThugBoy in Volume 1 appears again in Volume 2 trying to kidnap Empowered for Les Yay-related reasons. She then becomes a recurring character as a deliberate model for the fetish crowd that Emp keeps unintentionally feeding.
In the Fall Of Cthulhu comics by BOOM! Studios, a character with no speaking lines at all who can be spotted in a lot of backgrounds throughout the whole story turns out to be the final overmind (though not a villain per se) who orchestrated the whole story through a Gambit Roulette.
The Joker during Infinite Crisis. First seen torturing King and asking him why he wasn't invited to join the Society. Is told that he's considered too unpredictable, and kills King out of anger. Not seen for the next hundreds of pages or so. Guess who kills Alexander Luthor Jr.?
Before appearing as one of the lead villains in the Captain America Corps mini-series, Bright Star first appeared as an unnamed reporter in an issue of Ed Brubaker's Captain America run.
A zombie Deadpool appeared in Marvel Zombies, but only as an extra without dialogue. Later on, he plays a main role in the series. Similarly Black Bolt appeared numerous times in the series, but doesn't get an actual role until much later.
In Spider-Man, Norman Osborn was originally introduced as a nameless member of Mr. Jameson's club, and got upgraded to nameless friend of Jameson a while later. While he got a good deal of mostly non-speaking background appearances, he was barely noticed until he was revealed to be Harry Osborn's father about 2 years after his first appearance. 2 issues later he was revealed as the Green Goblin, who had been an active villain in the series for years.
John Constantine's official first appearance is in Swamp Thing #37. But in #25, there's a background character in a crowd scene who looks suspiciously similar to Constantine.
The first page of Watchmen features a red-haired man holding a sign that reads "The End Is Nigh." He appears a few more times and doesn't seem very important— until Rorschach's mask comes off halfway through.
In Downfall, Zommari shows up in chapter 16, casually mentioned: "The most senior of these artificial Arrancar, a bald, dark-skinned, sinister-looking man, was kneeling on one knee, silently, at the perimeter of the force." -he goes on to be a pivotal fighter in the subsequent battle, never mentioned by name. This is especially notable, as it gives him a much needed moment of true badassery.
In Time Braid, Demon Sakura is this. You think she's gone after a forced merge early on, but then she's discovered in a kind of 'inactive aspects' area of Sakura's Mental World, and Sakura uses her to guard the box containing the memories she doesn't want Sasuke to see. Later, her mastery of the Sharingan is used to give Sakura the chance at her Heroic Sacrifice, and afterwards she becomes half of Sakura's new demon/kami split axis.
In Forward, Ashley Frye bumps into a drunk man in a bar while looking for information about her sister Kaylee. This later turns out to be John Garis, an agent of the Academy who's after River, and he saves Ashley from Jubal Early.
In Calvin At Camp, Calvin throws a water balloon at Sally, early on in the episode "Champion Charlie Brown." She comes back later and has him arrested by the Urban Rangers for it, playing right into Lucy's hands.
In White Rain, the kid who gets punched in the face back in Chapter 1 shows up in Chapter 11 and helps out.
Calvin's dad nearly runs over a skunk in Calvin and Hobbes: The Series while on the way to a courtroom. Shortly after they arrive, it reappears and sprays him in revenge, forcing Calvin to take his place.
Dr. Watson and his wife have a baby girl in the finale for Children Of Time. The baby turns out to be a Time Lord, having been conceived in the TARDIS, and her regenerative abilities become instrumental in putting things to rights in the last episode.
The Powers Of Harmony: Vigil at first just seems to be a Sixth Ranger there for no reason other than giving the group of Royal Guards enough members. Then it turns out he's Horizon's brother (last seen, unnamed, in the flashback Blair and Piro show Twilight) and linked to him the same way as the Echoes.
Live Action TV
In Friends, "the girl from the Xerox place" is mentioned in multiple episodes starting in the second season. Later, Ross sleeps with the girl, ending his and Rachel's relationship.
In the first season of Dexter, Rudy is introduced in a justified manner but then given strange amounts of attention, developing his character until it is revealed that he is the Big Bad known as the Ice Truck Killer and, ultimately, also Dexter's brother, Brian.
Lots of characters in The Wire, most notably Clay Davis.
Just who the heck was that no-name crewman on Star Trek: Enterprise?? Nobody important, just a time-agent from a thousand years in the future who's secretly defending the Enterprise and its crew from interference from other time-agents trying to alter the timeline. Nothing really big...
Though this is a particularly inept version as he'd never actually appeared in the series before, so his sudden prominent role was a big tipoff that something was going on.
iCarly: Jeremy aka "Germy", a student who always coughs and sneezes is the prime example in Season 1. In "iNevel", after Nevel gave iCarly a dishonest review, the trio employs Jeremy to force Nevel to tell the truth, knowing his hate of germs. In "iWill Date Freddie", he also appears early in the episode, and later gets recommended by Freddie "who knows tech stuff" as his replacement when he left iCarly.
NCIS is a bit of a repeat offender on this one. If someone gets a line but doesn't seem to be contributing to the main plot otherwise, they did it. (If the writers try to hide their non-involvement by stuffing them into a romantic subplot with a main character, they definitely did it.)
Subverted in one episode, where the villain of the romantic subplot had not done it, even though he was suspected by a majority of the cast.
Oh, The Prime Suspect Never Did It. (Unless the prime suspect changes before the final ad break, in which case it was definitely the original suspect what done it.)
This can also be used in reverse... if there ARE no outstanding single line characters, the villain MUST be one of the major characters for the week. This is easily seen in a first season episode where the villain turned out to be David Keith, the sympathetic father and husband of the kidnapping victims and the very target of the plot!
This is the easy way to spot the murderer in CSI: Crime Scene Investigation. In the first 10 minutes or so there will be a completely unimportant background character, often who has one unimportant line. They add nothing to the plot, and would not be missed. Example: in one episode the owner of a diner is being questioned in her own establishment. Halfway through the chat she turned to tell the "short order chef" to get on with his work. I turned to my wife and said "It's the cook." It was.
The Miniature Killer, anyone? She appeared for about three seconds at the end of an episode, cleaning the floor in the lab, and later went on to be revealed as the killer.
Criminal Minds loves this trope so much they pulled it twice. In the same episode. The villain in Mayhem is actually two villains: the young teenage citizen who calls 911 to help Hotch, and the paramedic who comes to save them, violating the FBI's direct orders not to interfere.
Not to mention the second episode of the first season. the very innocent looking chemistry girl who explains the chemicals that could be used in arson is the one who actually stole the chemicals to commit the crimes.
Like Harry Potter, LOST loves casually mentioning random names who become important characters years later. Probably the most notable is Jacob, first mentioned in an offhand line of dialogue and who becomes mentioned dozens of times over the years as the Others' godlike figure. After numerous possible sightings, he finally appears in full for the first time in the season 5 finale. Radzinsky, Kelvin's former hatch partner who shot himself, became an important character three seasons later (due to time travel).
Ethan Rom, who had a brief appearance in a season one episode before the next episode revealed him as one of the Others. He then makes several other appearances throughout the series (despite being dead).
Ilana. She's introduced as merely a bounty hunter apprehending Sayid who crashes onto the Island. Turns out she knew where they were really headed, she works for Jacob.
The same thing happened to some random Mook of Apophis' in the Stargate SG-1 pilot. He didn't even get any lines until he saves all of the main characters near the end. Teal'c went on to join SG-1, and become one of only two characters to remain a main character for all ten seasons.
Meanwhile on Stargate Atlantis, the Ancient that becomes known to SG-1 as Merlin (Moros) slips in a cameo appearance nearly three years before he's even alluded to on SG-1.
In the Stargate Atlantis pilot "Rising", O'Neill's pilot (pun not intended) initially seems like a throwaway character... until he waltzes into the Antarctic outpost and it turns out that he possesses the Ancient gene, and is immediately recruited into the Atlantis Expedition. Turns out the pilot, Major Sheppard, is The Hero of the new series.
In later seasons of Battlestar Galactica a main plot point became that Starbuck had drawn a "mandala" religious symbol in her room which was visible in early season 2; they would then see this symbol on ruins they found, or in clouds as a "sign from God" and Starbuck would state she'd been doodling it since she was a child. However, in behind the scenes interviews, the writers admitted that the ring-shaped mandala symbol in her room in season 2 was just something the art department doodled, even they didn't think it was a "mandala" (just three rings), and the writers came up with the idea by rewatching old episodes and used it as a justification for major changes in the storyline...which in fact, were never planned out from the beginning. Fans eventually realized there was no over-arcing "Plan" to the series...
Another example from this show is the character Helo, who was meant to be a one-shot character in the pilot movie. He was well-received by fans, and there were enough inquiries about the fate of the character that they decided to keep him alive. He ultimately became an important character in the overall mythology of the series.
This might be evidence of a complete lack of planning, or just a willingness to change course based on feedback or spontaneous ideas that crop up later, while keeping other previously planned details intact. Word Of God was generally quite open about explaining in the podcast when something was spontaneous rather than planned, even down to changing the script based on actor improvisation.
Early episodes of The Sarah Connor Chronicles often showed someone watching the Connors, although usually all we could see was an arm with a barcode tattoo. Derek Reese (and, yes, he is related to Kyle) eventually became one of the series leads.
Frasier Crane's first appearance on Cheers (Season 3, Episode 1: "Rebound, Part 1") was as a nameless bar patron, until Diane sprung it on Sam that her shrink happened to be at the bar, observing them the whole time! Frasier (Kelsey Grammer) eventually stayed on long after Diane (Shelley Long) left the show, and eventually got his own spin-off.
Lampshaded in an episode of Monty Python's Flying Circus, when intergalactic blancmanges attempt to win Wimbledon. Two characters are introduced as "not the kind of people to be the centre of one of the most astounding incidents in the history of mankind... So let's forget about them and follow instead the destiny of this man." The couple then prove to be key to the resolution of the plot, and complain to the camera at the end of the sketch: "We tried to tell you at the beginning of the film but you just panned off us."
Subverted by the "Man in Members Only Jacket" in the last episode of The Sopranos.
Maybe not, considering how many people think he actually shot Tony.
Apparently, Steve Perry only let the show use "Don't Stop Believing" if no one died so in a way, Word of God says Tony survived.
Played straight by Tony's cousin, Tony Blundetto, whose actions in the fifth season are arguably the main catalyst for the New York-New Jersey War in the last season.
In the first episode of Firefly we see advertisements for the Blue Sun Corporation. A little bit later on, we see the characters using various products from them. It turns out that Blue Sun is one of the Big Bads that are peppered throughout the show, and their agents are a serious threat to our favorite crew.
Blue Sun was one of the results of Executive Meddling. Fox wanted a Big Bad, Fox got a big bad. They put the Blue Sun logo on the cargo containers in the pilot post-production.
Eagle-eyed viewers of the classic Degrassi Junior High will spot numerous "extras" milling around the school that would later go on to play a major role in the series. One of whom was Spike, who wasn't even named for some time despite evolving into the crux of the drama at the end of the first season and turning into one of the franchise's longest running characters. You can see her at the school dance in the second episode as a throwaway character... making out with the guy who would later be the father of her child.
The OC did the same thing with Taylor Townsend, who didn't become important until the third season but was clearly present in a number of earlier school scenes.
In the first half of Power Rangers Turbo, there was "A Drive to Win", which featured a soccer match. It unusually focused on a player named Carlos and a cheerleader named Ashley. A few episodes later, in "Passing the Torch", we are introduced to Cassie and T.J. who were riding a bus to Angel Grove, and later on we meet Carlos and Ashley again, and at the end of the two-parter, all four replaced the veteran rangers. It was revealed in an unproduced script called "Rangers in Concert" that Tommy, Kat, Tanya, and Adam did see the Millennium Message, thus knowing who their replacements are.
Similarly back in Season 2, Rocky, Adam, and Aisha were introduced long before they ended up becoming the new Red, Black, and Yellow Rangers.
In Kamen Rider Kabuto, for a good half-dozen episodes, a "tricked-out" rider, bearing a strong resemblance to Kabuto appears and even assists in fights (by out-doing the other riders' own Clock Up). We find out a bit later that this mystery rider is, in fact, Kabuto after his Mid-Season Upgrade.
In the fifth season of Angel, Wolfram and Hart's mailman is inexplicable wearing a Mexican wrestling mask at all times. A few episodes in, we learn that he was a member of a team of demon-hunting luchadores who fought an Aztec demon and a robot built by the Devil.
Very common in Monk. The office episode has to be a particularly egregious example: the guy didn't even talk before Monk suddenly singled him out as the killer. The baseball episode is a pretty extreme example as well, considering that the killer turns out to be someone Monk had seen appearing in an advertisement for a few seconds, not speaking, earlier in the case.
Another episode pulled this with the "gunman" being beneficial to the heroes. Monk and the detectives are investigating a bank robbery when Randy questions a living statue who was working outside the bank. Randy then is inspired to become a living statue himself and practices the trade throughout the episode, thus implying that the statue's role in the story is over. Later, the heroes are locked in the vault by the perpetrators. They later open a box which turns out to contain the controls for the electronic message board on the front of the bank. They use it to request help. Guess who relays the message to the police.
In Space Sheriff Gavan, during one episode Gavan manages to get to the victim of the day before the monster of the week kills him and gets him to safety. He'll live, but only if he gets medical treatment at Gavan's home planet. So he's shipped off to Planet Bird and never spoken of again, until he shows up during the final battle in a Big Damn Heroes moment as Sharivan the newest Sheriff. Turns out Da Chief of the Space Sheriffs approved of his toughness and had him inducted into the Sheriff (actually it was because they found out while treating him that was really the Chosen One for a supposed lost race of people.) He would go on to be the hero in the next series Space Sheriff Sharivan.
The Observer in Fringe appears as a bald Man In Black in the background of every episode that nobody seems to notice. In Episode 4 we learn more about him, and that he's somehow connected to the odd incidents that the main characters are investigating.
"Doctor Saunders" in Dollhouse. Not only do we find out that she's a doll, but when she reappears in "Getting Closer", she closes the episode by shooting Bennett Halverson (Summer Glau). So she's literally a gunman.
A one-off villain who tries to get Angel to off himself in Buffy the Vampire Slayer's third season, plus its minions who live under a Christmas tree lot, seems like a relatively innocuous villain of the week, until it all comes back four seasons later as the Big Bad.
The astute viewer probably should have been suspicious, though, since the baddie in question is apparently the "first evil", and you don't get to be the source of all evil without having something going for you.
Early in the series, there's Jonathan, a Recurring Extra who appears repeatedly around their high school. He's usually in some sort of distress and needs to get rescued. He later makes some prominent appearances in "Earshot" where Buffy prevents his suicide, and "Superstar" where he gets A Day in the Limelight. In season 6, he falls in with Warren and becomes part of the trio of villains for that season.
His season 6 cohorts, Warren and Andrew, count too. Warren was seemingly a one-shot character who apparently left town during his brief second appearance. Andrew is the till-then unseen brother of Tucker Wells, who was the antagonist in season 3's "The Prom". Tucker would've actually been there instead of Andrew and fulfilled Warren's role, but actor Brad Kane was unavailable.
An early episode of Babylon 5 introduces a Love Interest for Londo Mollari who leaves him to work out her personal life. Two seasons later, she reappears and is summarily killed as part of a plot by Morden to manipulate Londo into resuming his alliance with the Shadows. It works — meaning that a character who appears in three episodes (and spends one episode as a corpse, and another as a ghost) turns out to be critical in shaping the entire second half of the story.
Another very literal example is Jack, Garabaldi's second in command, who is present in his minor role through much of the first season. At the end of season 1 he is revealed to be involved in a plot to assassinate the President when he shoots Garabaldi in the back to prevent him from warning anyone.
Lucy Saxon from Doctor Who, quite literally. For almost two full episodes, she's nothing more than one of Harold Saxon's assets. Then she picks up the gun.
We first meet Wilfred Mott as he's running his newsstand on Christmas Eve during Voyage of the Damned, then he becomes much more important later on.
In the episode that introduces Martha Jones, an old lady keeps appearing in the background, asking various people for help while aliens are causing chaos, making the audience think she's just a confused and clumsy old lady. Then it's revealed that she's actually the blood-sucking villain the aliens are looking for.
Supernatural viewers may remember Adam Milligan, a boy that Sam and Dean meet who is teased at in Season 4 promos to possibly be their half-brother. Turns out, even though he '''was''' their brother he was Dead All Along and the boy the Winchesters meet is a Ghoul trying to kill them. Very few people expected to hear from him again... until a Season 5 episode reveals that even though Dean is the Archangel Michael's preferred vessel, he is not his only vessel. Being a vessel is In the Blood... and Dean just happened to inherit the trait from his father. Since Dean won't consent to possession (and he apparently has to, to be used by Angels), guess who is suddenly brought Back from the Dead? HINT: It's not John.
It's also implied that the only reason that this worked at all was because the time period was so short.
Crowley is referenced in passing by another crossroads demon in Season 3's "Bedtime Story" when she mentions her (male) boss to Sam. Season 5 revealed that Crowley had been the one Bela gave the Colt to in the third season. He gets mixed up in an Enemy Mine in Seasons 5-7 before becoming the Big Bad of Season 8.
Another Gunman for Supernatural would be the Trickster. He appeared in the second and third seasons as an antagonist with god-like powers and a veiled interest in the Winchester brothers, before the fifth season revealed that he is actually the Archangel Gabriel, who fell from Heaven when he couldn't stand his family's fighting anymore.
Sherlock: Molly Hooper introduces her new boyfriend, Jim, early in "The Great Game". In the last scene, he is revealed to be Moriarty.
"Did I really make such a fleeting impression? But then, I suppose...that was rather the point."
In The Reichenbach Fall, John finds Mrs. Hudson with a repairman after getting a report that she has been hurt. Later on, we find that the repairman is the hitman sent by Moriarty to kill Mrs. Hudson if Sherlock does not commit suicide.
Merlin includes a straightforward Chekhov's Gun with Excalibur, which is burnished by dragon's fire during the episode and thrown into a forest lake at its conclusion. The next season introduces a Mysterious Waif called Freya, who dies during the course of the episode and taken by Merlin to the same lake where he sets her body adrift in a small boat upon the water. The episode in question is called "The Lady of the Lake." You connect the dots.
Castle used to be in love with this trope. The killer was always the one person they didn't interrogate (especially if it was the grief-stricken relative). It's gotten better in the third season, though.
Charmed's third season had the background character of Abbey who worked in Piper's club who was there for about five episodes. Then in the episode Sight Unseen she is revealed to be Prue's stalker.
EUReKA has a minor example in the episode 'Minor Nobel'. Two elderly scientists shown trying to explain nuclear fission to Zoe later turn out to be members of the title character's team, without which he cannot save the world from an accidentally activated particle cannon.
In Community episode "Cooperative Calligraphy", it turns out Troy's pet monkey, who was seen in one episode the previous season, was the thief stealing Annie's pens.
In the Leverage episode "Girl's Night Out", the guy in background being a terrible waiter turns out to be the guy that planted the bomb.
In Once Upon a Time, there was an unnamed man introduced in the first episode of the second season. It wasn't until episode 6 that we find out his connection with Emma and Henry. And we don't find out that he is Baelfire, Rumpelstiltskin's son until episode 14.
"Daughter of Evil" by the Vocaloid Kagamine Rin gives us this example: Early on, the song mentions that the princess has a "servant with a like face". In the sequel, "Servant of Evil" by Kagamine Len, it turns out that the servant in question, the princess' twin brother, changed clothes with her so he could die in his sister's place.
Red Hot Chili Peppers released "Dani California" in 2006. The title character was soon revealed to be the same "Dani the girl" from the chorus of "By the Way" (2002) and also the "teenage bride with a baby inside" from "Californication" (1999).
Eugene from Foxtrot was this, as the page image suggests. He started out as a minor character in the 1997 Camp story arc, but 3 years later, the Wus, including him, returned, but aside for one strip early on, he never appeared. That is, until it turned out that he was the one who stole Phoebe's camp journal, and left a bunch of fake clues from everyone, setting up the events of the arc.
Also happens in Professional Wrestling as companies will use local talent or developmental wrestlers as crowd plants for heels to attack or other roles as police officers or security. Also happens if wrestlers have matches on the B-Shows before having a proper debut on A Shows.
Molly Holly actually made two appearances on episodes of WWF Heat back in 1998 under the name Starla Saxton. This was before she joined WCW and later WWE permanently.
Candice Michelle was introduced as a backstage make-up artist late in 2004 and appeared in random backstage segments for a while before becoming a prominent character on TV.
Another one that shows how well WWE creative team can plan stories in advance is the character of Tori (not Wilson). She was introduced as an obsessed Sable fan at the 1999 Royal Rumble helping Sable win a match and eventually feuding with her going into WrestleMania XV. Watching old Sable matches will show Tori sitting in the front row of the audience regularly for at least two months before she actually debuted on TV.
In 2003 the La Resistance stable was your typical Foreign Wrestling Heel team and one episode had them make their way to the ring and insult a man who appeared to be a US pilot. Later on in the match, the pilot jumped out of the crowd and entered the ring to help La Resistance win their match. Next week he was added to their stable as Rob Conway.
The NXT rookies from season 1 could count given that when the season was over, they rampaged WWE and formed The Nexus.
Even the McMahons followed this trope. From Vince's announcing days before the Screwjob outed him as the WWF/WWE's owner, to Shane's refereeing and appearances as a backstage official, to Stephanie appearing as a random passer-by in a Stone Cold Steve Austin segment months before debuting as Vince's daughter.
In Role-Playing Games, most RPGA tournament events followed this trope in that if someone was introduced passively, but by name, then that person would return by the end of the event either with the Superweapon or as the Big Bad. One player was heard saying at Gen Con: "Of course I knew he was the bad guy. He was the first NPC we met who was an ass to us."
Amara Li was named as a random museum donor in Pathfinder Society's 2nd season. In the 3rd season, she is the leader of a major faction.
In Noël Coward's Blithe Spirit, the one who called the ghosts into the house and is keeping them tied there turns out to be the maid, an overeager girl who for most of the play has just been your typical simple servant played for laughs.
Early on in Dirty Rotten Scoundrels, Chief of Police Andre warns Lawrence, a master conman, that there is an infamous con artist even more skilled than him in town, known as the Jackal. This is promptly forgotten about for most of the show until "The Reckoning," at the climax of the story: after Ms. Colgate, Lawrence and Freddy's con target whom both men had fallen in love with, leaves the scene, having supposedly been swindled out of $50,000 by Freddy, Lawrence and Freddy find that they are the ones swindled out of $50,000, with the lone suitcase they have remaining to them merely containing Freddy's clothes and a note from Ms. Colgate that says "Goodbye, boys; it was fun! Love, The Jackal."
Not quite. Lawrence is on the lookout for the Jackal in the beginning and once he sees Freddy conning some tourists, he assumes he's the Jackal. However, it was never officially confirmed that he was.
In Hamlet, Laertes is introduced briefly as a character in the first act, before departing for most of the play's storyline. He returns in the fourth act and plays a major role at the end of the play.
In Pippin, the torch-wielding player who will play a part in the grand finale makes a false entrance near the beginning of the play.
Played with a bit in Tom Stoppard's mystery parody The Real Inspector Hound, where both the murderer and the victim are Chekhov's Gunmen.
Rehearsal For Murderthe killer is the man in the back of the auditorium. Also true in the TV movie it's based on.
Inverted in the play Rumors when the two biggest players in the show never actually appear on-stage, with one of them only showing up with one line from off-stage at the end.
Jones from Gunnerkrigg Court. Her first mention in the comic was so subtle that no one noticed it at the time. Then she was introduced standing next to the Headmaster at the parlay, watching the proceedings silently. As it turns out, she's responsible for training the future Medium, and she's a valuable source of information.
In Tales of the Questor, there is a small story where Linneaus, a Raccoonan pastor learns that the Alligator people in the swamp were looking for information about God and he volunteers to go to them as a missionary. While that story seems like a postscript story to the strip's first major continuity, there is a later story where a wizard tells of a boy with a powerful talent for magic who goes half-crazed in horror of his power and the people who tried to exploit him and he was last seen running into the swamp, never to be seen again. These stories may be unrelated, but given the religious allegory nature of the strip, it would seem that the boy is inadvertently heading for the one Raccoonan who can help him.
Girl Genius: Krosp the emperor of all cats is in the last panel of This page among Dr. Demitri's teddybears.
Moloch von Zinzer at first appears to be just a throwaway enemy. In just a few short pages, he comes back to play a larger role. The clank in the time window doesn't actually come into being until years (our time and comic time) later. Von Zinzer's true importance is hinted at when Dupree gives her phenomenon report to Klaus.
Merlot is of minor importance, when we first meet him, and then one last time years later.
The Geisters... they first appear in the above-mentioned phenomenon report from Dupree.
Otilia, the Muse of Protection, appears in another body, then in a flashback cameo, then we see her somewhat worse for wear.
Franz, a huge lizardlike monster who lives in the sewers of Mechanicsburg was introduced trying to have a nap in june 2008. In december 2011, he awoke, and came to the defense of the Heterodynes.
During the Sister arc of El Goonish Shive, Tedd and Elliot found the diary of the wizard who created the diamond that had "created" Ellen. Guess who the antagonist of the arc Sister II is, six years later.
In an early Order of the Stick strip, Sabine mentions that she is a servant of "the archfiends" sent to aid (and get sex from) Nale. Later on, we see a brief flashback of her in the Lower Planes, where she receives orders from three rather ominous looking cloaked figures. These three figures were eventually reintroduced as characters in their own right, the Inter-Fiend Cooperation Commission, and look to be shaping up as very important villains...
And now we have Elan and Nale's father Tarquin, who only appeared in a single panel of a cutaway gag in one of the early strips.
For his early appearances in the story, Blackwing is the subject of jokes about how DND players neglect their familiars when playing as arcane casters. Then he plays a crucial role in O-Chul and Vaarsuvius' plan to destroy Xykon's phylactery, and gets a promotion to major character.
In 8-Bit Theater, the little kid who is orphanized by the Light Warriors is introduced and makes some minor appearances, until it's revealed that it's Sarda's past self.
Incidental characters in The Inexplicable Adventures of Bob! usually wind up with something more significant to do later on. Rocko Sasquatch is probably the best example, being introduced as just a quick joke—the huge scary guy Bob has to share a jail cell with for a couple of strips—and then returning two years later as a major character.
In Homestuck, from very near the debut of the first troll it was revealed that there were twelve of them, and in some panels of the kids' Pesterchum chumlists you can see their trolltags. All were introduced later; some stayed minor characters, others... didn't.
Then there's the alternate John who Terezi tricked into flying to his death. His death led to the Dave in his timeline going back and becoming Davesprite, but after that he was completely forgotten until dead Vriska meets him with a dream bubble, and thinking he's "her" John, takes him on a tour/date.
Oh look, it's a little guy walking across the desert. Oh, he's found something with a spirograph on it, hey, is that John? Oh, this Wayward Vagabond guy was the one talking! Aaaand he's going to be the one who fights Jack Noir.
John is described early on as having a deep-seated hatred for Betty Crocker. It's mostly played for laughs, until the Doc Scratch intermission of Act 5 Act 2, where it's revealed that Betty Crocker wasn't human, and is mostly likely the Troll Empress, working for Lord English.
The Empress herself is also a Chekhov's Gunman, having been referred to in Feferi's introduction.
In Act 6, we meet Jane Crocker, Nanna's teenage alternate. Her appearance was first previewed back in Act 4, two thousand pages and about a year and a half prior.
In Jake's letter to John, all the way back at the Act 4 epilogue, he mentions that somebody had to twist his arm to get him working on John's birthday present. Fast forward to Act 6, and Jake talks to Calliope, who mentions giving him some more arm twisting.
In one strip of Shortpacked!! a nameless woman working at a supermarket shows up. A while later she begins dating one of the main characters and became one herself. When the author went back and titled some of his earlier strips he called the one she appeared in "She'll Show Up More Later".
In one of the first story arcs of Demon Eater, we see a white giant. Later on, she's revealed to be a member of one of the strongest Demon Societies in the story.
In Prophecy Of The Circle this happens to a couple of tekk characters, mostly because the first chapter is told from the perspective of the tikedi, who are their enemies and can't communicate with them.
Renn'tekk, who first appears as a random, nameless tekk wrecking havoc in a tikedi village, but becomes an important character after the first perspective-flipped chapter.
Shan'rekk too doesn't get a proper introduction when he first appears, although in his case it's plainly visible that he's important, or at least a very unique tekk.
Like the FoxTrot example, in a Pv P murder mystery arc, Francis is briefly shown, then fades as suspicion shifts to "Tom Bolero." Francis turns out to be the murderer.
In Spacetrawler, the apex speaker (and apparent Big Bad) Kuu-Drahc is accompanied by an unnamed personal assistant when he heads a meeting of the GOB. Later, the protagonists learn that Kuu-Drahc is not the big bad, but takes orders from a Man Behind the Man named Qwahntoo. Then they find out that Kuu-Drahc's "personal assistant" from earlier was actually Qwahntoo.
In Narbonic there's a young, cute blonde woman wearing round glasses. We see her a couple times in a bar where Dave is doing something bizarre. She plays the 'straight man' character in the scenes. We don't know anything about her. Until the final arc of the webcomic, when her identity is absolutely critical.
"Octopus Pie" is practically made by this trope. Hardly a single character gets introduced without getting back to the comic later.
During a Christmas review, Linkara refuses to do Yet Another Christmas Carol, even though the spirits keep arriving. The Ghost of Christmas Yet to Come gets a reaction from him... "Is that a robot hand?" It's the first appearance of Mechakara within the reviews.
Two of them in Broken Saints. The first is the hobo Raimi meets near the alleyway, who seems to be nothing but another one of his hallucinations. The second is the supposedly dead Lear Dunham, one of the co-founders of BIOCOM. In the end, they turn out to be the same person. The freakin Big Bad.
Many, many people in Whateley Universe works. Given that the stories center around the 600 or so students at the Whateley Academy and their connections (plus the fact that the number of novels, novel chapters, short stories, novelettes, and vignettes now numbers over a hundred) it is sort of inevitable that characters seen in passing can become major players in later stories. Examples: Beltane (Kendall Forbes) gives the protagonists the campus tour on day one... and much later gets her own leading role in "For Whom the Belle Tolls", as well as other appearances. The Headmistress gives a speech on the first day of classes... and then turns out to also be the greatest superheroine around (in her spare time).
One of the hot blondes that Phase sees in the cafeteria on her first day at Whateley Academy - the one who really stares angrily at her — turns out to be an old enemy. Who then in later stories turns out to be the blackmailer. And then in a later story actually gets people to try to kill Team Kimba. And then in a later story takes over the Alpha clique and runs the student body, so she can really go after the heroes.
At first, Cavalier and Skybolt only get mentioned to show how dangerous The Don really is, and why The Don runs the campus. They're central to the Fey and Generator story "Christmas Elves". And then what they do next drives a lot of the plots for Winter Term.
One of the throwaway jokes early in the universe is about some girl at school who has the spirit of the squirrel and is a campus joke. She has now become a protagonist with her own stories, and in her combat final, she managed to beat one of the most dangerous bullies at Whateley in a simultaneous Crowning Moment of Awesome and Crowning Moment of Funny.
div This five minute skit uses it twice! (Pay attention to the chaos that effects 2 characters...)
During The Irate Gamer's review of Super Mario Bros. 2, he makes a joke about the game only having one player by having another Irate Gamer briefly appear, asking if he could play. Towards the end of his review, he comes back, revealing that he's an Evil Twin.
Two in There Will Be Brawl. Game and Watch had been seen around the city doing various tasks. He actually is an Eldritch Abomination, and is the "End of Days" meant to bring about the end of the world.
Ness and Lucas were seen playing in an alley, and served to remind Luigi of his motivation for fighting. Then it gets turned on his head when he discovers they are the murderers.
And that feeling of hope Luigi got from seeing them was artificially planted by their telepathy to keep Luigi fighting - which they found entertaining.
From the Global Guardians PBEM Universe: The tall, impressive looking woman standing just behind and to the right of crimelord Baron Samedi in the early story that introduced Samedi as a Diabolical Mastermind? Yeah, it turns out that she's more than just Samedi's Dragon. It turns out she's Battle, the mother of Stone, the former Global Guardian.
Lance M Donovan who had made appearances earlier in I'm a Marvel... And I'm a DC before his significance showed up. In literal terms, we also have the Punisher who shot the Joker when he was holding Harley hostage to use as his escape. You know when he said "I'm waiting for an opportunity to present itself", it was going to be awesome.
Averted with the Professor in Romancing Sa Ga 3. They have a unique sprite, are conspicuously introduced, and have two different quests associated with them. Most other characters with all these traits can join your party... but the Professor is just a minor NPC with no relevance outside their associated quests.
The Questport Chronicles: So, that mage who shows up in the first quest of the third year? Yeah, turns out that he was responsible for the destruction of Questport.
Survival of the Fittest: Evolution has Khalid Shamoun, a "winner" of a previous experiment run, who first appeared in the prologue, being shot by the scientists after mouthing off to show that they won't allow rebellion. Later he's put on the island as a player for the second time partway through. Another example, this time from the main site, would be Yelizaveta "Bounce" Volkova, who first appeared as a character in the in-universe chat and later made a appearance in the main game.
Eric Rosethorn from The Quest For Geekdom makes a brief appearance as a one shot character. Later he becomes the big bad.
Early in Project Million, Diamanda pops the balling of a little boy at Disneyland, then steals his lollipop. He later shows up to club her over the head and save Robert. Though he's really only after his lolly.
Most Literal Example Possible: The assassination of the Archduke Franz Ferdinand was the last straw that led to World War One, which led to the The Great Depression, which led to Hitler's rise to power, which led to World War II, which led to the Allies dividing Europe, which led to the Cold War, which led to the Russians invading Afghanistan, which led to the United States backing some unsavory types, which ultimately led to 9/11. Not often does one assassination get to define a whole century.
It may have happened anyway, Franz Ferdinand was just the excuse. Austria was going to invade the Balkans anyway. It is well documented, and public knowledge at the time, that the Balkans were a powder keg just waiting for a spark to set it off.
Way, way back in The Roaring Twenties, there was an unimportant art student which had been rejected from the Academy of Fine Arts in Vienna. He served in the German Army during WWI, and reached the unimportant rank of Lance Corporal. He joined a small, two-bit political party that was deemed dangerous by the police (he was originally a police spy, before the party won him over), but otherwise not even a blip on the political radar. This man's name? Adolf Hitler.
Following the Russian Revolution and the establishment of the Soviet Union, there was a low level enforcer in the Bolshevik Party with the almost unpronounceable name of Iosef Besarionis dze Jughashvili. He managed to quickly rise through the ranks and changed his name to the much easier to pronounce, Joseph Stalin.
A librarian at the University of Peking spent most of his free time reading and discovered some books by a guy named Karl Marx. This avid reader was named Mao Zedong.
There was also the carpenter from Galilee that became sort of important later on, as well as the Arabian merchant and the shepherd with the speech impediment.
Some obscure French officer, a prince from the backwater of Macedonia, and this Asian guy who had a horde or something. What's a khagan?
A 1916 newspaper printed a photograph of a little boy donating five cents to a fund for war orphans. That little boy was Richard Nixon.
Gerald Ford was a no-name lawyer who won a congressional seat in a surprise upset, and got introduced to the nation almost two decades later thanks to a speech he gave on the House floor in which he criticized the Vietnam War, as well as the numerous insults President Lyndon Johnson hurled at him in response. A few years later, he was the 38th President of the United States.
The vast majority of elected officials, especially those from notably humble origins such as Abraham Lincoln and Barack Obama, although humble origins are not a requirement: John F. Kennedy and George W. Bush were less important sons of powerful men who did not carry the weight of expectations that their siblings did... at least, not at first.
After the assassination of President Abraham Lincoln on April 15, 1865, his funeral procession would travel from Washington, D.C. to his (almost) final resting place in his hometown of Springfield, Illinois (since his coffin has been exhumed numerous times afterward). One of the procession's stop would be on 14th Street and Broadway in New York City, on April 24, 1865. A picture was taken of this procession, and an open window is shown in the left-hand side of the photo. You can barely see, but two little boys are leaning out the window watching the procession go by. Those two little boys? They're future President Theodore Roosevelt and his brother Elliott Roosevelt, father of Eleanor Roosevelt.
US television has done this too. Jeffery Donavan (Michael Weston) from Burn Notice and Frederick Weller (Marshall Mann) from In Plain Sight both had an appearance on Monk before starring in their own series'.
Summer Glau had a guest spot in the Joss Whedon Angel before starring in Firefly.
One scary example comes in the form of Ted Bundy's background before he became one of the most infamous serial killers in modern American history. Years before his spree, he was a lowly intern lawyer who got caught up in a political scandal. Bundy gave an interview to the local media smiling, laughing, and denying any involvement in the scandal.
In 2010, the San Fransisco Giants claimed outfielder Cody Ross for the sole purpose of keep him away from the division leading Padres, who were in desperate need of an outfielder. They planned on using him as a late inning defensive replacement. But he managed to make the postseason roster and become a pivotal part of their World Series team, winning NLCS MVP
Some of the most famous generals of World War II fought during World War One (George Patton, Charles de Gaulle, Bernard Montgomery, Erwin Rommel, among others).
A lot of famous movie directors' could be described as this. Case in point, in 1953 a little-known photographer who had made a few short films and documentaries released a somewhat cheesy feature film titled Fear and Desire. That man later went on to direct 2001: A Space Odyssey, A Clockwork Orange, and The Shining, amongst other incredible films.
In 1959, the director of the now-forgotten Roman epic Gli ultimi giorni di Pompei (The Last Days of Pompeii) fell ill and another man, some guy named Sergio Leone was brought in to replace him at the last second. Several years later, Leone was given a simple job- create a simple, low-budget Spaghetti Western re-using an old set to make up for the failure of a previous project. Looking for a cast he hired an actor at that point best known for his role in the tv series Rawhide. They worked together on this project, using what little they had, and created a film that turned out to be a surprising box office success, so the studio gave them a bigger budget for a sequel. They worked together once more, and created a second film that was even better, and got an even bigger budget to create yet another film- and they made The Good, the Bad and the Ugly, considered now one of the greatest movies ever made. The actor's name? Clint Eastwood, who would go on to direct a number of movies himself and win a number of Academy Awards.
In 1974, bad marketing resulted in the failure of college short-turned-feature Dark Star. The writer, disappointed about the results, decided to retool the script using the simple idea of a spaceship's crew chasing an alien. He ended up giving the script to an unsuccessful director who re-wrote the protagonist into a woman and decided to cast a young stage actress- and in 1979, the film was released under the title of Alien, propelling Ridley Scott and Sigourney Weaver to stardom.
King Edward III of England had four sons: Edward of Woodstock, Lionel of Antwerp, John of Gaunt, and Edmund of Langley. None of these sons became king after him, but are nonetheless extremely important because their progeny ended up fighting each other in the Wars of the Roses.