Vilgax is a Chimera Sui Generis, he is an intergalactic warlord and will stop at nothing to gain the Omnitrix from Ben 10. Vilgax was first seen attacking Xylene's spaceship in an attempt to retrieve the Omnitrix from her ship. He was severally injured in the attack and was confined to a regeneration tank for much of the first season and would often send drones or bounty hunters to attack Ben and retrieve the Omnitrix. When he came out of the tank his body was modified to increase his physical structure. Vilgax finds Ben and and kidnaps him and attempts to steal the Omnitrix. He is rescued by Grandpa and Gwen and battles Vilgax on top of Mout. Rushmore. At the end of the battle. Vilgax's ship self destructs while in orbit and crashes. It was later revealed that Vilgax has been to Earth before and fought Grandpa when he was a member of group that battles supernatural threats. In the second season Vilgax was found to have survived the explosion of his ship and had been shot into space. He was later found by Kevin 11. The two teamed up and tried to take the Omnitrix from Ben. The battle ended with the two being trapped in the Null Void.

Vilgax reappeared somehow escaping the Null Void in Ben 10: Secret of the Omnitrix. It was revealed that he destroyed the Petrosapien home-world home to Diamondhead's species by the petrosapien Tetrax. He was defeated when Azmuth, the creator of the Omnitrix activated a giant alien called Way Big and Ben threw him into space.

Vilgax was incinerated in a gasoline explosion caused by Ben and his dad, it is unknown if Vilgax survived, but due to his history of surviving and escaping dangerous situations he will probably seen again.