Who he is: Jimmy, a.k.a. Leech
His power: Jimmy can negate the X-gene of any mutant that comes near him.
His story: Jimmy plays an integral role in X-Men: The Last Stand as the source of the mutant cure that drives the film’s narrative, but he’s not much more than a plot device. Jimmy’s background is a mystery, and all the audience learns is that he’s a patient of Dr. Kavita Rao, who uses his DNA to create the cure. Kitty Pryde is sent to rescue Jimmy during Magneto’s attack on Worthington Labs, but Jimmy ends up saving her life when he turns off Juggernaut’s invulnerability, knocking out the villain when he charges into the wall of Jimmy’s cell. Free from Worthington Labs, Jimmy becomes a student at Xavier’s School For Gifted Youngsters, where he will ideally learn to control his powers so he’s not going around turning off the thing that makes everyone special.
Played by: Cameron Bright
Currently, Leech is: In the revised timeline following X-Men: Days Of Future Past, Jimmy probably hasn’t been born yet, if he’ll even be born at all.
Where will we see him next? There are no plans for Jimmy to reappear, but the comic-book Leech was introduced in the ’80s, so maybe a different version of that character will show up in the next ’90s-set X-sequel.