Eon

Eon is an inter-dimensional time traveler and one of Ben's secondary villains and the arch-enemy of Professor Paradox. He became an evil alternate version of Ben 10,000 after absorbing multiple Bens from multiple timelines.

Appearance
In Race Against Time, Eon wears a black helmet with a purple tinted visor. His main outfit is a black bodysuit, over which he wears a long dark coat. He also has black gauntlets with purple highlights on them. When Ben becomes a copy of him, he lacks the helmet.

In Ultimate Alien, Eon wears a silver helmet with a purple visor that blocks all view of his face, leaving only two glowing purple eyes visible. He retains the black bodysuit, but has silver boots, gauntlets and a chestplate instead; a purple cape is also hanging off his shoulders. He is actually an evil version of Ben 10,000.

In Omniverse, Eon appears to be highly advanced in age (or just repulsive in appearance). He retains the black helmet with its purple visor, but his face is visible through it, much like in Race Against Time  He retains the silver gauntlets and boots but there is also silver shoulder pads on his black jacket. He wears a black bodysuit which has some purple lines and a silver collar that covers his entire neck.

Early Life
Eon was sent to the Earth to activate the Hands of Armageddon and start the invasion on Earth. In this timeline Eon was too old to activate the Hands (and grew older each jump through time), so he hunted the Omnitrix wielder to duplicate his DNA and then control the DNA copy, but was stopped by Professor Paradox everytime. He later was captured by the first Earth Plumbers 200 years before the original series and was captured by cryogenic freezing.

Ben 10: Race Against Time
Eon has a plan to activate the Hands of Armageddon. He uses ape-like aliens to help him use the Omnitrix to turn Ben into a younger version of himself showing some control of the watch, due to the fact that the Hands of Armageddon needed the energy of a young Chronian to activate. He also deactivated the fail safe so his DNA would completely overtake Ben's personality, essentially changing Ben into a clone of himself and leaves the scene of the crime seemingly wiping himself from existence as "two of the same beings cannot exist in the same place at the same time". As Eon, Ben activates the Hands of Armageddon which will start an alien invasion, but returns to normal after Gwen manages to reach Ben inside young Eon. The real Eon appears again and tries to exact his revenge, but Ben as Wildmutt, manages to send Eon crashing into the Hands of Armageddon, destroying it in that timeline in a huge explosion of bright purple-colored glowing energy.

Ben 10: Ultimate Alien
In Ben 10,000 Returns, it turns out that Race Against Time was in an alternate timeline. As it turns out, Eon survived his battle against the Ben of that timeline, and has since been traveling through various different timelines, enslaving different versions of Ben wherever he finds them. When he comes to the real Ben (20 years from Ultimate Alien), Ben 10,000 used Clockwork's abilities to send him 20 years earlier, to present day Ben. They eventually find out that he was absorbing the Bens, making them into his minions, and that he's a corrupt Ben Tennyson, wanting to eliminate all other Bens and become the one and only Ben in the whole space-time continuum. They realized that Eon was hunting them from inside their Ultimatrixes. However, Eon was defeated when the Hands of Armageddon was destroyed by Jetray. Paradox states that all the Bens Eon had absorbed will go back to their own timeline and return to normal.

Ben 10: Omniverse
Eon returned in Omniverse in Ben Again, where he has been trapped in the main timeline by Paradox. Seeking to get hold of the time-walker's Chrono-Navigator in order to have the freedom to traverse the multiverse once more, Eon goes after Ben as both his Child self and Teen self at the same time, he touches their Omnitrixes, causing the immature 11-year-old Ben to switch minds with his more mature 16-year-old self. Realising Paradox won't show up in the present day because the 11-year-old mind of Ben doesn't know him, Eon quickly heads five years into the past, where he ambushes Paradox and cuts off his robotic right hand. Taking Paradox to a different dimension, Eon interrogates him and, knowing that Paradox never lies, figures out that his missing hand was his Chrono-Navigator. Originally planning to go back to the moment it was severed, Eon is warned against doing so by Paradox as it risked throwing him out of exist due to the fabric of reality being stretched thin by both of their presences and the switched minds of Ben.

Eon instead heads for the present day, where he steals the Chrono-Navigator from the immature Ben after he finds it. Immediately, Eon summons his minions, but the time portals don't seal after them. Paradox, seen through another portal, reminds Eon that he DID warn him that tampering with time would lead to disastrous results. As both times were now visible through the distortions he created, Eon was blasted by two versions of Clockwork and sent out of the time line, restoring it to normal and erasing all the events he had just caused to occur.

Ben 10

 * Ben 10: Race Against Time (first appearance)

Ben 10: Ultimate Alien

 * Ben 10,000 Returns (first re-appearance)

Ben 10: Omniverse

 * Ben Again (first re-appearance)

Trivia

 * Eon's motivations and plans in Ben 10,000 Returns are similar to those of the DC Comics supervillain Gog. Both are villains who travel through time and across dimensions, slaying alternate versions of a superhero wherever they find them. However, unlike Gog, who outright kills all the alternate Supermen he comes across, Eon simply enslaves all the Bens he runs into.
 * The enhanced version of Ben 10: Race Against Time states that Eon's previous attempts to get to Ben were thwarted by Professor Paradox.
 * An eon is a time measurement unit that involves multiple eras and is equal to one billion years.
 * Eon is one of the few personal enemies of Paradox; he's clashed with Paradox many times in many different timelines, each never being able to defeat the other.
 * Eon and Paradox's relationship is similar to the relationship between the Doctor and the Master.