Vilgax is the overall main antagonist of the Ben 10 franchise.
He is Ben Tennyson's archenemy and a Chimera Sui Generis conqueror that has conquered many planets and wishes to claim the Omnitrix for himself and conquer the entire universe. He is a past enemy of Max Tennyson and, later, would become the enemy of Ben Tennyson, once he finds out that Ben wields the Omnitrix.
In the original series, he served as the main antagonist of Season 1, the secondary antagonist of Season 2, a supporting antagonist in Season 3 (as a futuristic version of himself), the main antagonist of the film, Ben 10: Secrets of the Omnitrix, and the main antagonist of the non-canon Season 4 finale, Goodbye and Good Riddance. In Ben 10: Alien Force, he serves as the main antagonist of Season 3. In Ben 10: Ultimate Alien, he serves as the secondary, later true main antagonist of Season 3. In Ben 10: Omniverse, he serves as a supporting antagonist in Arc 3, the main antagonist of the Arc 4 finale, And Then There Was Ben, and a supporting antagonist in Arc 8, serving as the secondary antagonist of the series finale, A New Dawn. He serves as the main antagonist of the Ben 10 Reboot series.
In the original series and Ben 10: Omniverse, he was voiced by Steven Blum, who also played Starscream. In Alien Force and Ultimate Alien, he was voiced by James Remar. In the 2016 reboot of Ben 10, he is voiced by Yuri Lowenthal.
Vilgax is extremely cruel, ruthless, arrogant, authoritative,arrogant and power-hungry. Vilgax always wants to conquer the entire universe, using Omnitrix which he views as ultimate weapon.