Ben was originally a ten-year-old boy who grew up in Bellwood; he was unpopular to his classmates and often bullied in school by two boys named Cash and J.T. However, his life changed the day he went on summer vacation with his grandfather, Max and his cousin, Gwen. That evening, they stopped to camp in the woods. Ben witnessed the crash of a strange capsule from space, which happened to contain the Omnitrix, a powerful watch-like device.
As soon as Ben found the device, it firmly affixed itself onto Ben's left wrist, and Ben was unable to remove it. At first scared, Ben soon discovered that, using the Omnitrix, he was now able to transform into ten super-powered alien creatures, and began to use the device to become a superhero. Though he occasionally arrested ordinary criminals, he was quickly led to also fight super-villains, starting with Dr. Animo, Kevin 11, and ultimately, Vilgax, a vicious and evil alien warlord who would stop at nothing to get the Omnitrix for himself.
Despite being very immature and occasionally using the Omnitrix for minor selfish purposes, Ben proved to be a valuable wearer for the Omnitrix, defeating Vilgax and saving people several times.
Ben's favorite aliens are Four Arms, Heatblast, Wildmutt, XLR8, and Diamondhead, showing his tendency to favor brute force over well-thought plans. This was especially apparent when he was examining 16-year-old Ben's Ultimatrix; he called NRG and Big Chill "lame", Brainstorm and Goop "weak", and Humungousaur "okay" due to his big size and stature.
In Ben 10: Secret of the Omnitrix, during a battle with Dr. Animo, Ben accidentally activated the Omnitrix's self-destruct and rushed off with Gwen and Tetrax Shard to find the Omnitrix's creator. He was joined by Myaxx and later learned that the countdown sped up when he transformed. He learned he could be a hero without the Omnitrix. Ben then discovered the creator of the Omnitrix, who was really a Galvan named Azmuth. Azmuth shut down the self-destruct and gave Ben access to a new alien, a massive form named Way Big. With Way Big, Ben easily defeated Vilgax and hurled him into space.
In Ben 10: Destroy All Aliens, it is the end of the summer vacation (as well as after the events of the previous movie) and Ben, Gwen and Grandpa Max spend their evenings fighting aliens on the streets of Bellwood. During a battle against a robotic tank, Ben as Upgrade and Gwen argue about the best way to defeat it, leading to Gwen using a magenta/pink-colored dismantling spell on the tank while Ben is attached to it. Unknown to the children, this leads to a malfunction in the Omnitrix. Later, after a mishap in the school he attended where the Omnitrix accidentally teleports his homework, Ben is grounded by his parents and forced to stay home and do a history report. Ben attempts to work on the report before the Omnitrix teleports his laptop away as well. Shortly afterwards, Tetrax Shard arrives and tells Ben that Azmuth has asked to meet with him. They go to meet Azmuth but are attacked by an evil version of Waybig. Tetrax and Ben fight the alien, who is also teleported into the Omnitrix, though neither of them is aware of it. Tetrax decides to take Ben to search for Azmuth and activates a new function on the Omnitrix. Before he can explain this new ability, the ship is attacked and Ben is sucked out into the atmosphere, falling to the ground as Diamondhead. It is later revealed that the new ability prevents Ben from reverting back into normal when he times out, simply transforming between alien forms. Ben as Fourarms arrives at Stonehenge and is attacked by a weaponizing Galvanic Mechamorph who demands to know about the alien that attacked Four Arms. Four Arms tries to explain he knows nothing, but the Mechamorph only continues to attack and the Mechamorph's teleporting ability causes the pair to carry their battle across the globe, destroying part of Stonehenge and nearly damaging Cristo Redentor in Rio de Janeiroand fighting at the Great Pyramids in Egypt before arriving back in Bellwood. Ben transforms into Grey Matter and manages to escape the Mechamorph. Meanwhile, Gwen and Grandpa Max receive a call from Ben's parents Carl and Sandra informing them that Ben has escaped the house. They go in search of him, only to find Tetrax and discover Azmuth's ship. Looking at the ship's log, they discover that Azmuth disguised it as a semi truck to track down and fix the malfunctioning Omnitrix, but crashed and was destroyed by the evil Waybig. After escaping the Mechamorph, they soon encounter Ben back at his house and Tetrax restores Ben's Omnitrix to revert Diamondhead back into normal just as the Mechamorph catches up to them. Gwen sees how the Omnitrix reacts after Ben returns to human form and deduces what has happened just as she, Ben, Tetrax and the Mechamorph are transported into the Omnitrix itself. Inside, Ben and the Mechamorph continue to battle before being attacked by a swarm of Stinkflies just as Gwen and Tetrax are ambushed by a herd of Wildmutts. The four catch up with each other and they realize that the evil Waybig is inside with them just as he resurfaces. The Mechamorph, who is revealed to be Azmuth's father, attacks the Waybig in revenge for killing his son while Gwen explains to Ben about the malfunction that she caused to the Omnitrix when she cast the dismantling spell on the robotic tank while Ben was attached to it. She uses Azmuth's father to reverse the transportation and return them to Earth. Unfortunately, the Omnitrix malfunctions again and transforms Ben's parents into Wildmutt and Heatblast, causing Gwen to realize that the evil Waybig is Azmuth himself. Leaving Grandpa Max and Tetrax to handle his parents, Ben and Gwen follow Azmuth's father and Azmuth to the city park where Ben transforms into Waybig to subdue Azmuth and hold off his father while he and Gwen try to reverse the transformation. Between the two Waybigs, they do a few hundred million dollars in property damage from smashing huge building after huge building (there are most likely no one in the buildings as the battle takes place in the morning before people arrive to work in them, which may be why they are not concerned about huge loss of life). They soon convince Azmuth's father that his son is the very alien that they are fighting and the three work together to convince Azmuth to regain control of himself, use his father's Mechamorph abilities to fix the Omnitrix and transform Azmuth back into normal. Azmuth reprimands Ben and Gwen for their errors and reveals his father is a Galvan wielding a Mechamorph-type armor. Returning to Ben's house, Azmuth restores Ben's parents to normal and repairs the Rust bucket, previously destroyed in the battle, before leaving to reconcile with his own father. Ben's parents, having forgotten that they grounded Ben, tell him to enjoy his fishing trip with Grandpa Max and Gwen. Ben declines, having learned to be more responsible, and stays home to finish his history report for school. The movie ends with Ben, Gwen, and Grandpa Max on another road trip where they encounter Dr. Animo again and the three prepare for another exciting battle.
10-year-old Ben appeared in the Ultimate Alien episode The Forge of Creation. He looks different from how he did in the original series (due to Ultimate Alien's different art style). He now has a face that resembles the current Ben but appears slightly thinner. His cargo pants are shaded with a lighter shade of green and his shoes are different, and his skin tone resembles the present Ben's as well. Also, he is even less well behaved than the Ben from the original series (who was already obnoxious and immature).
Ben had continued to use the Omnitrix to encounter and defeat different types menaces both terrestrial and extraterrestrial in origin in addition to going on adventures with Gwen and Max (or occasionally by himself or with some other allies along with Gwen and Max) a year later when he (along with Gwen) was 11 years old.
- Ben Tennyson/Five years prior to Omniverse
- Ben Tennyson/Alien Force
- Ben Tennyson/Ultimate Alien
- Ben Tennyson/Omniverse