Marvel’s Gladiator is one of the publisher’s strongest heroes. He possesses similar abilities to Superman, including super strength, durability, speed, heat vision, and flight. But while he is vulnerable to certain forms of radiation, his major weakness doesn’t involve a Kryptonite-like substance. Rather, it’s his confidence level. The more the Gladiator loses hope in victory and feels his internal struggles rise, the weaker he becomes.
Gladiator’s unique vulnerability was first revealed in “Fantastic Four” #250 (by John Byrne, Christie Scheele, and Joe Rosen), where he believes he’s fighting Reed Richards. In actuality, he attacks a disguised Captain America who defends himself with his indestructible shield, and when Gladiator’s powerful optic beams have no effect on “Mr. Fantastic,” he questions himself, allowing the Invisible Woman to knock him out. Upon defeating the Shi’ar soldier, Reed notes that since Gladiator’s powers are psionic in nature, he becomes weaker when he doubts his own abilities.
In a fight with the invulnerable X-Men hero, Cannonball, in “Uncanny X-Men” #341 (by Scott Lobdell, Joe Madureira, Tim Townsend, Steve Buccellato, and Richard Starkings), Gladiator unleashes his full might on the mutant and doesn’t cause a dent. As a result, his confidence is shaken, and he immediately becomes vulnerable to his opponent’s responding attack. Cannonball swiftly takes him out, despite the noticeable power difference between them. In short, to defeat Gladiator, his enemies need to make him believe, if only for a moment, that he’s not a Superman-level threat.