Vilgax

Vilgax is an intergalactic alien warlord and conqueror, a Chimera Sui Generis who serves as Ben's archenemy, and the most recurring villain in the on-going franchise. He was introduced in And Then There Were 10, and has since appeared in all the seasons of the original series (however, the only season 3 episode he appeared in was Ben 10,000, as well as season 3 of Alien Force, Ultimate Alien, and Ben 10 Omniverse.

Vilgax was the main antagonist of the first three series (Ben 10, Alien Force, and Ultimate Alien).

Background
A vicious galactic warlord known as "the most dangerous being in the universe", Vilgax's goal is to get the Omnitrix (Original) and use it to create an army capable of transforming into any alien to conquer the universe. Though he originally chased Ben only because of this, and had few concerns about his fate once he had the Omnitrix, the several failures the boy caused him, as well as an imprisonment in the Null Void, his hatred for Ben grew to the point that in his latest appearances, he seems to want to kill him as much as, if not more than, getting the Omnitrix.

Vilgax is one of the most feared beings in the universe, having conquered ten planets, destroyed five others and created a black hole. In fact, he is so feared, that almost no organic life form is willing to work for him, forcing him to use Drones for his crew, though he is able to find mercenaries willing to work for him for the right price.

Personality
Vilgax is ruthless, cruel, and power-hungry. His primary objective seems to be obtaining the Omnitrix (Original), so that he can use it to take over the universe. He is known to hold a grudge; most notably against Max Tennyson and his family. He is also known to be very manipulative, notably so of the Galactic Code of Conduct, in order to achieve his goals. After escaping the Null Void, Vilgax seemed to have gone partially insane, as he was enraged more easily and exhibited facial ticks. He appeared to have recovered by Alien Force.

While stranded on Earth following his defeat at the end of Alien Force, Vilgax skillfully manipulates a group of humans known as the Flame Keepers' Circle into serving him. Upon discovering that his squid-like form resembles the alien of knowledge worshiped by the cult, he adopts the role for his own and manipulates his new followers into helping him escape the planet.

Despite his cruel and villainous tendencies, Vilgax does care about his own people (taking his role as Vilgaxia's ruler and champion very seriously), so much so that he is willing to put his own life on the line and use whatever other means necessary to ensure Vilgaxia's and its people's safety; even if it means begging his enemies for help.

Vilgax is shown to be highly afraid of Ma Vreedle as seen in Vreedlemania.

Background
In the year 1773, Vilgax had been exiled from his homeworld for "ambitious disobedience." He is summoned to Earth by a distress signal sent by a time-traveling Maltruant. There, he makes repairs to Maltruant's damaged transport in exchange for a Chronosapien Time Bomb that he would use And Then There Were None|some time later. During this, Vilgax encounters George Washington and a time-traveling 16-year-old Ben Tennyson. Watching Ben transform into various aliens is what initially fostered Vilgax's interest in the Omnitrix.

Back when Max Tennyson was still a young Plumber, Vilgax was stealing warheads from a military base. Max and his partner Phil showed up. In the resulting fight, Vilgax was stuck to a nuclear warhead by Max, and launched into his own ship. At that time, Vilgax was only slightly larger than a human man, compared to his now colossal size, an addition to his cybernetic augmentation.

Ben 10 Omniverse
A robot replica of Vilgax appears as an enemy.