Instances of Small Role, Big Impact in Comic Books.
- 100 Bullets:
- Arms dealer Abe Rothstein appears in precisely one issue of a 100-issue series (Issue #89), and he's killed at the end of that issue. In said issue, though, we learn that he was the source of Agent Graves' attachés all along. His death signals the end of Graves' "game" with the leaders of the Trust.
- Joan D'Arcy is one of the less seen Trust heads and the last one to be formally introduced. However, her hiring of the man that kills Rothstein and Javier Vasco is the lynchpin for the beginning of the end.
- Ace of Space: The Slogons only appear in the first issue, but are responsible for the whole plot due to killing the alien who held Ace's power-granting belt, thus leading to him acquiring it. The alien also fits, due to dying within the first couple pages of the first issue but empowering the hero.
- A non-human one in Allergic. The unnamed puppy that Maggie goes to adopt on her tenth birthday is only seen there at the shelter. Her encounter with them breaks her out in hives and itching, so they leave the puppy behind—and she finds out she's allergic to animal dander and can't have a dog at all.
- In Bamse, two characters fit into this in Vargen's sad backstory. The first one is a lady, who recognizes the very young Vargen as the boy, who helped a gang of thieves with stealing her purse, so she calls the shop where Vargen works and gets him fired. And there is also the shop-keeper himself, who tells poor Vargen "once a thief, always a thief" before he fires him. None of these two characters had more than a few lines, but by refusing to give a young orphan a second chance, they were the ones who made Vargen become the most infamous criminal in the area, until Bamse was able to make him reform many years later.
- Batman has Joseph Chilton aka Joe Chill, an average thug who once tried to rob a rich family in an alley, and ended up killing the two adults, but couldn't bring himself to shoot their young child. That family was the Waynes, and his parents' deaths were what motivated Bruce Wayne to create the 'Batman' identity to make sure that others wouldn't suffer like he had. Chill himself is small potatoes and tends to get unceremoniously killed off whenever the story is told, assuming an adaptation in which his actions aren't given to a more important character (e.g. in Batman (1989) the Waynes' murderer is Jack Napier, who then becomes The Joker), but had he not tried to mug the Waynes, Batman would never have existed.
- The Blue Streak: Scarface only appears in the first issue, but inspires the hero's superhero career by killing his brother.
- In Diabolik the Minister of Justice of Clerville rarely appears, no matter who holds the post, but has two important roles:
- Just by existing in the background he makes sure that Ginko remains on Diabolik's case and is not replaced by lesser cops, as Ginko is the only one who actually has a chance with Diabolik in spite of his many failures.
- In Clerville no execution may happen without his authorization. Thus every time Diabolik is arrested, his continued survival depends by how fast the Minister and his staff can write down the death warranty and sign it, to the point that in occasions he expected to arrest Diabolik for sure Ginko has called the Minister beforehand to have him write down the warrant and reduce the time Eva has to break Diabolik out.
- Empowered: Imperial Pimpotron Alpha graces all of six pages yet leaves two major legacies: Empowered's body image issues, and the Imperial Cosmichains that Emp later uses to subdue and seal a similarly sesquipedalian supervillain whose stay proves significantly more substantial — Demonwolf.
- The Golden Age: Super-powered Nazi Parsifal only appears briefly in the opening montage and in a flashback when Manhunter gets his memories back. However, his ability to neutralize superpowers kept the Allied meta-humans out of World War II, shaping a lot of the postwar story. Thompson being credited with killing Parsifal helps kickstart his political career and Manhunter (the real killer of Parsifal) got a case of plot relevant amnesia during his mission to kill Parsifal and other Nazi leaders.
- Green Arrow villain Veronica Dale, aka Hyrax, was a minor villain who appeared in a single story before dying, but in that single story she accomplished what no other villain had ever been able to do: she killed Oliver Queen. And he stayed dead for eight years, pretty impressive for a B-list hero.
- Justice League of America: Martian Manhunter villain Commander Blanx appeared in a grand total of two JLA stories. In the first of those stories, however, he engineered the destruction of the entire Martian race, transforming J'onn J'onnz from the jovial crime fighter he was in the Silver Age and into the introspective loner he is today.
- MonsterVerse:
- Camazotz, who only appears in the Godzilla vs. Kong prequel graphic novel Kingdom Kong, has a pretty big impact on the bigger MonsterVerse overall, as he's directly responsible for the destruction of Skull Island and all wild specimens of its local life via enclosing a Perpetual Storm over the island. This kicks off Kong and Team Kong's entire arc in the movie.
- To an even larger extent, Shinomura, who only appears in the prequel graphic novel Godzilla: Awakening and yet is the entire reason for Monarch's existence. Without Shinomura, the events of all four movies and all five graphic novels would not happen.
- Pat Patriot: America's Joan of Arc: The foreman only appears for one eight-page issue, and doesn't even get a name, but he's responsible for Pat's superhero career by firing her, which led to her exposing his smuggling operation.
- The Green Goblin in The Pulse. He's only in a few issues, but it was his final unmasking.
- Scooby-Doo! Team-Up: The Great Gazoo. He shows up at the end of the crossover with The Flintstones to send the meddling kids back to their own time but he mistakenly sends them to the Jetsons' time, allowing the next issue to happen.
- Spider-Man:
- The villain Belladonna appeared for all of one plotline, and wasn't much of a challenge for Spider-Man. The wall-crawler crossed paths with her when she tried to kill a Corrupt Corporate Executive who had ruined her business. The name of that executive? Roderick Kingsley, alias the Hobgoblin. Belladonna's attempts to murder Kinglsey left him determined to never be that vulnerable again, prompting him to look for ways to defend himself. The Hobgoblin went on to become one of Spider-Man's defining villains in the 1980s, in his prime ranking with the likes of Norman Osborn and Doctor Octopus.
- Emil Gregg, the compulsive confessor in Eddie Brock's backstory. Gregg falsely confessed to Eddie that he was the serial killer known as the Sin Eater, a story Eddie published in his newspaper the Daily Globe. However, Spider-Man captured the real Sin Eater, exposing Gregg as a fraud and turning Eddie into a laughing stock. This resulted in Eddie's Irrational Hatred of Spider-Man which he tried to purge by going from church to church, praying for forgiveness. One of those churches turned out to be the place where Spider-Man had left the alien symbiote costume he had acquired in Secret Wars (1984) and the rest is history.
- The unnamed crook who killed Uncle Ben only had one other appearance, and isn't even named in his first appearance, but if Peter had caught him instead of letting him go, Ben would never have died and Peter would never have become a hero.
- Star Wars: Legacy has Arc Villain Zenoc Quah, a treacherous Yuuzhan Vong Shaper. He only physically appears in a three-issue arc and is killed off at the end of it, but he sticks around just long enough for it to be revealed that it was he who sabotaged the Ossus Project and framed both his own race and the Jedi for it, kicking off the entire plot.
- The Steel Fist: Ludlow only appears in the first issue, but he's responsible for the Steel Fist's existence, due to his mutilating the hand that ends up being empowered.
- Superman: Derek Marlowe was a minor crook who debuted in the Starfire's Revenge arc and was killed off one issue later, but Supergirl spent years dealing with malfunctioning powers because of the depowering pill he slipped into her drink during his single appearance.
- Bob from The Walking Dead is only in two issues and initially seems to be around for a minor Pet the Dog moment for The Governor. His second appearance has him reveal his Hidden Depths as a former Army Medic and has him save The Governor's life after Michonne tortures him, allowing him to attack The Prison and kill half the cast.
- The Wraith: Silky Weaver only appears for one half of one issue, but is responsible for the entire comic due to killing our hero, who rises from the grave to stop him.
- Dr. Bolivar Trask in X-Men. He appeared in exactly three issues before his death in a 1965 issue, but his creations — the Sentinels — regularly menace the X-Men to this day, and they serve as a potent symbol of anti-Mutant prejudice. Many of his surviving relatives are also major supporting characters in the X-Men mythos: his son Larry appeared in a notable Roy Thomas arc, his daughter Tanya (aka "Madame Sanctity") is the leader of the Sisterhood of the Askani, his brother Simon is a famous anti-Mutant activist, and his nephew Donald (himself an example of the trope) helped Cassandra Nova decimate the population of Genosha in New X-Men.
- Yellowjacket: Jake Mallon only shows up for the first issue, but he ends up kickstarting Vince Harley's superhero career by leaving him to be stung to death by bees, causing our hero to discover his control over them.
