Vilgax (Classic)/Ben 10

Vilgax first appeared in And Then There Were 10, where he is seen shooting at Xylene's ship to recover the Omnitrix, forcing Xylene to throw it down to Earth and causing the main plot of the series. His limbs were all destroyed because of the battle thanks to one last-ditch attack that hit the main bridge of the Chimerian Hammer, requiring him to be placed by his drones in a repair tank for healing.

As the series progressed, Vilgax soon discovered the Omnitrix had been taken by someone else (though ignoring exactly who it was), and made several indirect attempts to get the device back. This includes sending Drones from his ship, hiring bounty hunters (Tetrax Shard, Kraab, Sixsix and Rojo by fusing her with one of his drones). In the latter, he was able to shortly establish a telepathic link with Ben when the boy was fused to Rojo as Upgrade, warning him he was going to come for him one day.

Eventually, his body was repaired and cybernetically enhanced in Secrets, making him far taller and stronger than before. He then went on Earth to get the Omnitrix by himself. Ben's aliens proved to be no match for him, and Vilgax captured him. Though surprised to see the one who had caused him so many problems was just a human child, Vilgax revealed his plan for the Omnitrix to Ben and attempted to extract the Omnitrix from him, seemingly by sectioning his arm with an alien tool. After several complications, including interruption from Gwen and Max and Ben losing control of his transformations, the Chimerian Hammer exploded, seemingly with Vilgax still aboard.

At the end of the second season, Vilgax is still alive, having survived the destruction of his ship by teleporting out just before the explosion, but having been frozen as a result. He is found encased in ice by Kevin. Discovering Kevin's connection with the Omnitrix, Vilgax decides to team up with him in another attempt to retrieve the Omnitrix, however both are locked away in the Null Void dimension by the end of the episode.

A dream version of Vilgax appears in the episode Perfect Day, where he appears to confront Ben. The battle lasts for a short time, and then Vilgax tries to send Ben to the Null Void. As Four Arms, Ben throws him in instead, but this proves to be an error on the part of the Forever Knights, as Vilgax was about to send Ben to the Null Void without first obtaining the Omnitrix. This is the reason why Ben found out that the battle with "Vilgax" was just a set-up.

Vilgax reappears in Ben 10: Secret of the Omnitrix, where he once again attempts to retrieve the Omnitrix, having somehow escaped the Null Void (the enhanced version of Secret of the Omnitrix revealed that he stumbled on a Null Void portal being opened and used it to escape). During a flashback, Tetrax reveals that Vilgax destroyed the Petrosapiens' home world, and he (Tetrax) unwittingly gave Vilgax the final element needed to carry out his plan. Vilgax refers to his anger at having been trapped in the Null Void (including showing a short nervous twitch at its mention), which has deepened his grudge against Ben to the point where he refuses to acknowledge the danger threatening the universe if the Omnitrix self-destructs (but nevertheless gains enough respect for Ben to the point of calling him by his first name instead of his last name). He confronts Ben on Tetrax's ship and attacks him, only to be shot out into space through the airlock. He is finally defeated when Azmuth, the creator of the Omnitrix, gives Ben access to a massive alien, Way Big, who hurls Vilgax into outer space.

Five years prior to Omniverse
A flashback occurs where Vilgax is seen with a tied-up 11 year old Ben. Vilgax then threatens to feed Ben to his numerous Squid Monsters, but Ben breaks free and transforms into XLR8. The flashback ends with XLR8 being grabbed by a Squid Monster.