Gladiator

Kallark leads the Shi'ar Imperial Guard, a unit Claremont and Cockrum designed as an affectionate parody of DC's Legion of Super-Heroes, which makes Gladiator their Superboy analogue: flight, invulnerability, heat vision and strength enough to hold his own against the Hulk or Thor. His defining quirk is that his power scales with his conviction, so a Gladiator who doubts himself is beatable and a Gladiator who does not is nearly unstoppable.

He is a soldier before anything else, and Marvel has repeatedly put him in the impossible position of enforcing orders he despises, including presiding over the trial of Jean Grey on the Moon. After War of Kings he ascended to Majestor, ruling the Shi'ar Empire himself, which turned the empire's most obedient weapon into the man responsible for its decisions.

Gladiator arrived in X-Men #107 in 1977 during the Phoenix and Shi'ar arc that established Marvel's cosmic side of the X-Men mythology. He presided over the trial of Jean Grey on the Moon in the Dark Phoenix Saga, and has clashed with the X-Men, the Avengers, the Fantastic Four and the Guardians across decades.

War of Kings in 2009 changed his position permanently, elevating him to Majestor of the Shi'ar Empire. Later stories have used him as a reluctant ruler, still the strongest being in the room and no longer able to blame anyone else for what the empire does.