Alien X is still at work here, so some information may be incorrect, incomplete, or just plain missing!
Jennifer Kendra "Jen" Tennyson is an alternative Omnitrix wielder who wields an Ultimatrix, allowing her to not only transform into various alien species, but also allows her to evolve them into their ultimate form. She's rather arrogant and as a result, her universe's Azmuth never deemed her worthy of the final version of the Omnitrix.
Like Ben with Feedback, she had an unhealthy obsession with her transformation Solarstorm. At a younger age compared to most Ben's in the known multiverse, Jen unlocked Clockwork, causing Eon to avoid her believing she's more trouble than she's worth - in an accident relating to Clockwork, Jen accidentally sent her universe's Charmcaster six years into the future.
Kidd Blaster is a former deadbeat bounty hunter who spent his days orbiting Earth and pirating cowboy movies from them when the Omnitrix caused him to crash land on Earth. After his partner in crime, Rad-Is (A Galvanic Mechamorph), hacked the watch to remove the DNA lock, Kidd decided to make the most of his situation and become an Earth hero.
Kidd wields a Prototype Omnitrix, which is heavily damaged as a result of Rad-Is' hacking attempt. As a result, the DNA samples were scrambled. This resulted in Kidd possessing only nine transformations, all of which, Ben never acquired. In addition to the Omnitrix, he utilizes Sundance, a rapid-fire laser pistol, Butch, a stun baton that generates an electric charge upon contact with an enemy, and wears a durable armor that allows him to survive in almost any atmosphere.
Jason Nyathi "Kia" Thirteen, is an alternative Omnitrix wielder who obtained a much-improved version of his universes Omnitrix after a misfire by Azmuth that landed outside Jason's house. Intended for his universes Ben Tennyson, Azmuth sent Ben to take back the Omnitrix and despite defeating Jason, saw potential in him, giving Jason access to thirteen transformations and calling him "Jason 13" due to his age. By age 17, he has access to about five hundred thousand transformations and the ability to instantly switch through transformations with no timeout, although he still does not have complete access to Master Control.
Jason is incredibly cheerful, not having to go through much trauma in life despite his powers. This however can lead to him underestimating his opponents, but he generally knows when to get serious. He is a natural leader, quickly moving up the ranks of his universes Plumbers and becoming a Magister at the stunning age of 18.
Azmuth heavily disagrees with Jason wielding the Omnitrix, but trusts Ben enough to keep Jason under his wing.
Khan Blake found his Omnitrix around the age of 14 on a beach in Australia in 1951. He started naming his aliens early on when his sister called his first alien Boombox and this has stuck as a tradition ever since.
At the age of 18, he had the Omnitrix removed by the Plumbers so he could join the army. He left after five years and joined the police force for two years before the Plumbers came to him and asked him to put the Omnitrix back on. He reluctantly did so and began working for them as a special detective.
His creator has remarked that Khan hates anything to do with Tennyson's from other timelines.
The vast majority of Khan's transformations are name as references to pre-2000s pop culture. He is inspired by Constantine from DC, James Bond, Rorschach from Watchmen, and Eliot Stabler from Law&Order.
Ben 10finity is a composite version of Ben Tennyson created by Kuro the Artist while he was making a point regarding the Ben 10 vs Green-Lantern Death-Battle video. He is designed to be an absurd composite of every iteration of Ben Tennyson, with every ability that any version has ever possessed.
Aside from his Master Control Transformations, he utilizes the Ultimatrix and the Biomnitrix, allowing him to evolve and fuse his transformations. The Sword of Ascalon gives him additional reality-alteration powers, and Skurd can surrogate another transformation's powers. While his Ultra Ben visor is just for looks, the Potis Altiare multiples all of his powers even further. He also retains his ability to use magic.
In a dark timeline within the Omniverse, Dr. Ivo "Eggman" Robotnik defeats his universe's Sonic the Hedgehog once and for all and fulfills his dream of world domination. But his "dream", was short-lived, as another evil force rose and without a hero to stop it, Eggman himself was subjugated by a greater threat. He remained imprisoned for years, but built himself up physically until he gained superhuman physical abilities and proceeded to escape a prison specifically made to contain him and his great mind.
Free and with a new perspective on life, Eggman went into hiding, venturing to other worlds in order to find powers his foes would have no counter against. After decimating every facility and foe in his path, Eggman confronted the leader of this great evil. During the final battle, Eggman revealed his greatest trump card dubbed the "Egg Timer" a genetic alteration device that allowed him to change his genetic code. Using the device's Mobian form, "Blasthog" and shards of the now destroyed Chaos Emeralds, he finally defeated the great evil.
With the deed done, Eggman removed Blasthog from the device, built a memorial for his old archenemy Sonic, and left his dimension entirely to start a new life. Now known as Omegga, the Wanderer of Worlds, he would travel from across the Omniverse, stopping outside evils from encroaching on unsuspecting worlds.
His Omnitrix-like device, possesses unique characteristics uncommon to most Omnimatrix devices. Due to the origin of the device, it does not possess the DNA from the standard Omnitrix database. In addition, the Egg Timer's playlists are sorted into "cartons" of twelve rather than the standard playlist of ten. The Egg Timer also possesses a special battle mode dubbed "Shell Metal" forms, where his transformations acquire special armors based on various Eggman mechs from his past.
On Ben's 18th birthday, Azmuth refused to grant him access to the Master Control, as he didn't believe Ben was ready. Frustrated with this outcome, Ben decided to take matters into his own hands and figure out his own Master Control. Ben ended up deconstructing the Omnitrix and connected it directly into his brainstem, mimicking the automatic quick-changing features of the Master Control, but at a great cost. When Ben transforms, his brain is altered to match the primal instinct of the species he is using, turning him into a mindless killer with every transformation.
His relentless, primal nature forced Azmuth to hold him captive in a maximum security prison built to contain him by Azmuth. He spends his days reminiscing about all he has lost. After being in prison for so long, he decides to transform into Alien X, but since his transformations have no way of connecting to Ben's mind, doing this is essentially suicide, leaving Bellicus and Serena sitting in Alien X for all of eternity without Ben.
Azmuth feels immense regret for what had happened, considering it his biggest failure.
Bishop Tenson worked in the sheriff's department for many years to help maintain law and order. When a local group of bandits were fed up with his meddling, they took him to a mining ravine to eliminate him once and for all. However, a malfunctioning alien craft happened to be flying overhead carrying a gold mine of alien equipment.
One such piece of equipment was an extremely early prototype of the Omnitrix, created by the tinkerer, Azmuth. The malfunctioning ship, eventually blew up, spreading alien technology across the wild west. The Omnitrix attached itself to Bishop's arm and accidentally turned into his Pyronite transformation, The Burning Man. His captors were burned alive and he was presumed dead along with them. Their deaths being blamed on a freak TNT accident.
Bishop now wanders the wild west, using the alias, "The Shifting Phantom", to track down all of the missing alien technology, and to enforce the law across the land.
Eleanor "Ellie" Lee Chase is an alternative Omnitrix wielder who wields the Omnitrix's G7 model.
She is from an alternate universe called Dimension-1010 where everything is like the Prime Universe except one major thing, this universe's Ben died when fighting this universe's Vilgax and destroying his black hole generator Vilgax placed on the Earth.
Weeks after that moment, Ellie stumbled upon a plumber base by accident when she was in her local Max's Plumbing store. When trying to escape without being noticed, she went into the armory and found the Omnitrix which suddenly attached to her. When she was caught by the Plumbers, she managed to escape while trying to figure out the Omnitrix.
After knowing what the Omnitrix is and what it does (the same way Prime Ben figures it out), she then realizes that she was wielding Ben's new Omnitrix before he died. This results in her making a solemn oath that she would fill in the role that Ben made as a superhero, though she did keep her identity a secret.
She was a vigilante until the Plumbers found her and wanted to recruit her to being a deputized agent after seeing her fight villains and helping others which she did accept.
Her Omnitrix has twice the transformations Ben has, with having 130 transformations and having master control, months after Ellie gained the Omnitrix including Meltdown, Glass Cannon, Archangel, and Chop Shop. She did rename some aliens, however. One example being Benwolf who she named "Subwolfer" instead.
Ellie is calm and collected, though she does have a temper and can be naïve.
The Azmuth of the Gammaverse created the Omnitrix (Later known as the Gammatrix), but its use as a peaceful, observational device proved to be ineffective. Azmuth was commissioned by the Galvan army to turn the Omnitrix into a weapon, and so he did. He took the Omnitrix and modified it to become more of a weapon, but in order to stop his creation from becoming a weapon of mass destruction, he put gamma radiation into the Codon stream to stop the army from using it for war. This proved to be unsuccessful as it simply mutated the alien DNA instead of taking the DNA away. Azmuth then dubbed it the Irradiated Omnitrix, later known simply as the Gammatrix.
Through unknown means, the Gammatrix's creation reached Vilgax, who led a raid on Galvan Prime and stole it. Albedo, who wanted to make his mentor proud, snuck onto the ship and stole the Gammatrix back. However, when trying to escape, his escape pod was attacked and he was thrown far off-course, eventually causing him to crash land on Earth. He died in the crash, unwilling to use the Gammatrix to save his life beforehand. The Gammatrix is eventually found by Alexander Tennyson and curiously, put the Gammatrix on his wrist.
Putting gamma radiation inside the Codon stream means the DNA inside of the Gammatrix now changes the aliens transformations abilities and physical appearance, with some looking drastically different from what they normally appear in the universe, while others appear more or less unchanged.