Despite Thragg’s strength being unrivaled throughout most of “Invincible,” when the series reaches its end, there’s an argument to be made that Mark Grayson has taken the title of strongest Viltrumite for himself. As the story ends, “Invincible” flashes forward 500 years into the future, where the titular hero becomes Emperor Mark Grayson of the Viltrumite Empire. He’s brought peace to his people and rules alongside his wife, Atom Eve, with their daughter, Terra.
While his powers aren’t fully revealed, one of the most significant indicators of strength among the Viltrumites is the passing of time. Considering Mark is hundreds of years older and stronger, defeated Thragg in their past battles, and sits atop the Viltrumite throne, there’s a case to be made that he ends up the most powerful Viltrumite as the series concludes.
Mark might have leapfrogged Thragg in strength as the “Invincible” story ends, but it’s somewhat open to interpretation. It will be fascinating to see what approach the “Invincible” animated series on Amazon Prime Video takes, as whenever the show finally concludes, it can answer the question of who is the strongest Viltrumite more definitively than the comic book ever does.