Aggregor

Aggregor is the new villain in the Ben 10 series starting with Ben 10: Ultimate Alien. He first appeared in the Ben 10: Ultimate Alien first episode, Fame. He first appeared after Ben defeated one of his captors, Bivalvin, and then captured him. He had five alien captors: Bivalvin, Galapagus, P'andor, Andreas, and Ra'ad, and intended to absorb all of their powers. In the 10th episode of Ultimate Alien, he took his captors to Los Soledad to finally absorb their powers and succeeded (after ignoring the warning from Ben's former nemesis and current best friend, Kevin). The reason for absorbing his captives is to gain their powers (to become Ultimate Aggregor) in order to find 4 pieces of an artifact called the Map of Infinity in order to find a place known as the Forge of Creation.

He finds the first piece of the Map of Infinity in the episode with the same name in a temple full of traps on a planet that's half sun like, and half frozen. He finds the second piece of the map on the episode Deep. He finds the second piece on an all water planet. The third piece is found on Where The Magic Happens, where he takes the piece from the warlord from Charmcaster's home dimension (also the warlord that Aggregor took the piece of the map from is the same spieces as one of his alien captors, Galapagus). The fourth and final piece of the map is found in a planetoid known as the Perplexahadron in the episode with the same name from it's gurdian known only as The Sentinel. He finally finds the Forge of Creation in the episode with the same name and his "Ultimate Prize" was reveiled to be a newly born Alien X (on of Ben's restricted aliens). He fights off both 10 and 16 year old Ben, Gwen, and Kevin, then procides to absorb the newborn Alien X. But when he was about to absorb ultimately unlimited power, he was stopped by a once again mutated Kevin having absorbed the Ultimatrix from 16 year old Ben to stop him (even though 10 year old Ben offered him to absorb his Omnitrix), and then after he had gotten Aggregor away from Alien X, Kevin then absorbs Aggregor's powers as well, reverting Aggregor back to his normal state and was laying unconcious. After that, Aggregor's fate is left undetermined.

Background
Aggregor's race is the same as Ben's current friend, Kevin (they're both a race called Osmosian. But Aggregor is full osmosian and Kevin is half). His powers are mostly the same as Kevin's, matter absorbtion and energy manipulation. He used his powers to activate a time transporter to absorb his captor's powers and succeeded. He's more of a intergalactic threat than Ben's ultimate nemesis, Vilgax. Like Vilgax though, Aggregor also uses droid minions.