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No one escapes Aggregor.
Aggregor is the main antagonist of the first half for Season 1 of Ben 10: Ultimate Alien. He is an alien warlord who seeks five aliens in order to absorb their powers so he can obtain the Map of Infinity allowing him to enter the Forge of Creation so he can absorb the powers of a Baby Celestialsapien, and use it to become omnipotent and conquer the universe.
He was voiced by John DiMaggio, who also played Bender in Futurama.
A violent, arrogant, manipulative, and malevolent Osmosian, Aggregor's evil was that which made even Ben Tennyson take him seriously. Sadistic, unsympathetic, ruthless, and callous, Aggregor's selfish pursuit of power has destroyed many innocent lives, and was remorseless over kidnapping peaceful aliens if only so he could abuse their powers for his own advantage. He is willing to do whatever it takes to get his powers, even if he has to betray, manipulate, and kill to get his way.
Aggregor, despite his cunning nature, is also a coward. He even tried to absorb the powers of a Baby Celestialsapien despite it being defenseless. Overall, Aggregor is a selfish, unfettered madman who does not even have the excuse of turning insane like Kevin.
Aggregor's race is the same as Ben's current friend Kevin (they are both members of a subspecies of humans called Osmosians). His powers are mostly the same as Kevin's-matter absorption and energy manipulation. Aggregor is also noted for his high intelligence, demonstrated in how he tricked the protagonists to reach his goal for him, and his genre savvyness. He used his powers to activate a time transporter to absorb his captor's powers and succeeded. He is more of an intergalactic threat than Ben's ultimate nemesis, Vilgax. Like Vilgax, though, Aggregor also uses droid minions.
Ben 10: Ultimate Alien
Aggregor first appeared in the Ben 10: Ultimate Alien first episode "Fame". He first appeared after Ben defeated one of his captives, Bivalvin, and then captured him. He had five alien captives: 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 captives 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 four 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 in the episode "Deep". He finds the second piece on an all water planet. The third piece is found in "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 race 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 its guardian known only as the Sentinel. He finally finds the Forge of Creation in the episode with the same name and his "Ultimate Prize" was revealed to be a newly born Celestialsapien. He fights off both 10 and 16-year-old Ben, Gwen and Kevin, then proceeds to absorb the newborn Celestialsapien. But as he was about to absorb ultimate 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 left him laying unconscious. After that, Aggregor's fate is left undetermined. It was later revealed in "Night of the Living Nightmare" that he is currently incarcerated.
Ben 10: Omniverse
Aggregror did not appear in the fourth series, but is mentioned in a few episodes.
Aggregor is the first main villain to have been defeated by someone else rather than Ben Tennyson. The second is Diagon.