Ben was originally a ten-year-old boy who grew up in Bellwood; he was unpopular 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 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.
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.