Colossus shows up for a grand total of three minutes in X2: X-Men United, during which he saves Siryn from being kidnapped, armors up on-screen, beats the crap out of several soldiers and offers to help Wolverine. The character proved to be so popular with moviegoers and fans that he returned as one of the six team members (although several of his scenes were cut) who take part in the final battle in X-Men: The Last Stand, and gets a few badass action scenes in X-Men: Days of Future Past. However, his appearance in Deadpool, where he has a larger role than all his previous films combined, may be his most popular yet, thanks to how hilariously Adorkable he is.
Despite little characterization beyond being Magneto's lackey, Rebecca Romijn's take on Mystique got more praise as the years went by, as many prefer the Dark Action Girl persona to her Adaptational Heroism in the prequel trilogy.
Yuriko has barely any role in this film beyond acting as Stryker's mind-controlled bodyguard, but her incredible fight scene with Wolverine and her tragic death made her very popular. There were even plans to bring her back in the sequel, though it was canned when Bryan Singer declined to direct it. Fans would have to settle for a small Shout-Out in X-Men: Days of Future Past, when a Sentinel briefly uses her power to impale Sunspot.
Nightcrawler's father Azazel, who appears in the prequel X-Men: First Class, is a rather popular character, due to being, basically, Nightcrawler with red skin. Sure beats his really lame comic version.
Kitty Pryde a.k.a. Shadowcat became one in between the second and third movies - thanks to the character's appearance in the X-Men: Evolution cartoon. So her role is greatly expanded and she's widely thought as one of the better parts of Last Stand. Being played by a pre-Juno Elliot Page helps too.
Wade Wilson. Not Deadpool, oh no, but critics and fans pretty much unanimously praised Ryan Reynolds as pre-experimented Wade Wilson; when the much Truer to the TextDeadpool movie was finally made, it would have been ridiculous had they picked someone other than Reynolds to portray the title character.
Despite his short amount of screen time, Gambit has been well-received. Sad that he couldn't get his own movie.
Blink is one of the highlights of the movie because of her unique look and creative uses of her power in the action scenes. Most fans predicted this, since the character's comic counterpart is already a pretty big fan-favorite, and for the exact same reasons, no less.
Evan Peters' Quicksilver appears in only one part of the movie (breaking Magneto out of prison), but his fun, mischievous personality endeared him with many and the "Time in a Bottle" sequence is considered one of the best X-Men movie scenes ever. He got more screentime in the sequels, and became the second actor to reprise his character in the MCU in WandaVision although it ends up being subverted as he was just a civilian named Ralph Bohner brainwashed by Agatha Harknessnote Its also worth pointing out that unlike J. Jonah Jameson Jr. from Spider-Man: Far From Home, Quicksilver already appeared in the MCU, being played by Aaron Taylor Johnson.
In Deadpool, Negasonic Teenage Warhead won plaudits for being an Emo TeenDeadpan Snarker who hilariously contrasts both Deadpool and Colossus, and can kick plenty of ass too. She's certainly already more popular than her original C-List Fodder comic book self.
Logan: The doctor who treats Logan following his encounter with X-24, being one of the few humans to knowingly treat mutants with genuine decency, even thinking it an honor to meet one, and is quite possibly the only adult human with lines to survive the movie.
Many fans thought Peter stole the movie. Though he dies pretty soon after joining the team, The Stinger has Deadpool save him from his death via a time travel machine.
Yukio is very well-liked despite her limited presence. Her cool power set, upbeat personality, the fact she makes even DeadpoolSquee at the sight of her, and that she's a lesbian that doesn't act stereotypical or offensive has earned her a large following. In fact, some were disappointed we didn't get to see more of her.
Dark Phoenix: Dazzler's surprise cameo at the party managed to dazzle a number of fans.
