Sentry

Sentry debuted in 2000 in a Paul Jenkins and Jae Lee miniseries that revolutionized the superhero concept at Marvel. Robert Reynolds discovers he is the world's most powerful hero, with the power of a million exploding suns, but that the entire planet forgot his existence because his alter ego, The Void, threatened to destroy everything Sentry protected.

This premise of tragic duality — the more good Sentry does, the more destruction The Void causes — turned the character into a metaphor for mental illness and internal struggle. Brian Michael Bendis incorporated him into the New Avengers, and his role in Marvel's Siege represented one of the most impactful moments in modern comics.