Vilgax is an intergalactic alien warlord and conqueror, a Chimera Sui Generis who serves as Ben's archenemy, and the main antagonist of the franchise, having appeared multiple times in every series. Ben considers him as one of the most dangerous villains he has faced. Vilgax was the main antagonist of Ben 10, Season 2 of Alien Force, and Season 3 of Ultimate Alien.