Cyclops
Wolverine may be the most famous member of the X-Men, but Cyclops is the definitive X-Man. He's essentially the main character of the franchise since day one, and has one of the most complex arcs of any major superhero. Scott Summers' story begins with him being a straight-arrow hero and protege of Charles Xavier, but over time he deviates from Xavier's dream to develop a radical, separatist, militaristic version of the X-Men in the name of protecting mutants. Recently he crossed a horrible line by accidentally killing Xavier his father figure! in a fit of rage while possessed by the Phoenix, and has become an outlaw revolutionary and a pariah among his old friends. Everything about Cyclops comes down to two essential metaphors that he's a man who is always struggling against his own body to stay in control of a destructive power, and that his myopic obsession leads to all his triumphs and all his failings.
Oh, and then there's his gloriously messy love life! His relationship with Jean Grey as a young man is fine but after she dies for the first time, he goes off and impulsively marries a woman who looks exactly like her we later find out she's a clone but he abandons her and their infant child immediately after learning that the real Jean has come back to life. He's a total cad. And then he ends up having a psychic affair with Emma Frost while he's married to Jean Grey, and shacks up with Emma immediately after Jean dies for a second time. He's a mess. And seriously, what is up with him only getting seriously involved with incredibly powerful psychics? And why does his intense rivalry with Wolverine often seem weirdly sexual?
Anyway, Cyclops is frustrating and profoundly uptight and wonderful and probably the best superhero ever.