Ben Tennyson (Classic)/Ben 10

Originally, Ben was a 10-year-old boy who grew up in Bellwood. He was unpopular to his classmates and was often bullied by two boys named Cash and JT However, his life changed when 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.
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 was the end of the summer vacation (as well as after the events of the previous movie) and Ben, Gwen and Max spent their evenings fighting aliens and criminals on the streets of Bellwood. During a battle against a robotic tank, Ben as Upgrade and Gwen argued about the best way to defeat it, leading to Gwen using a magenta/pink-colored dismantling spell on the tank while Ben was attached to it. Unknown to the children, this led to a malfunction in the Omnitrix. Later, after a mishap in the school, the Omnitrix accidentally teleported his homework. Ben was later grounded by his parents and forced to stay home and do a history report. Ben attempted to work on the report before the Omnitrix teleported his laptop away as well. Shortly afterward, Tetrax arrived and told Ben that Azmuth asked to meet with him. They went to meet Azmuth but were attacked by an evil version of Way Big. Tetrax and Ben fought the alien, who was also teleported into the Omnitrix, though neither of them were aware of it. Tetrax decided to take Ben to search for Azmuth and activated a new function on the Omnitrix. Before he could explain this new ability, the ship was attacked and Ben was sucked out into the atmosphere, falling to the ground as Diamondhead. It was later revealed that the new ability prevented Ben from reverting back into normal when he timed out, simply transforming between alien forms. 
Ben as Four Arms arrived at Stonehenge and was attacked by a weaponizing Galvanic Mechamorph who demanded to know about the alien that attacked Four Arms. Four Arms tried to explain he knew nothing, but the Mechamorph only continued to attack. The Mechamorph's teleporting ability caused the pair to carry their battle across the globe, destroying part of Stonehenge and nearly damaging Cristo Redentor in Rio de Janeiro and fighting at the Great Pyramids in Egypt before arriving back in Bellwood. Ben transformed into Grey Matter and managed to escape the Mechamorph. Meanwhile, Gwen and Max received a call from Ben's parents Carl and Sandra informing them that Ben had escaped the house. They went in search of him, only to find Tetrax and discover Azmuth's ship. Looking at the ship's log, they discovered that Azmuth disguised it as a semi-truck to track down and fix the malfunctioning Omnitrix, but crashed and was destroyed by the evil Way Big. After escaping the Mechamorph, they soon encountered Ben back at his house and Tetrax restored Ben's Omnitrix to revert Diamondhead back into normal just as the Mechamorph caught up to them. Gwen saw how the Omnitrix reacted after Ben reverted to human form and deduced what had happened just as she, Ben, Tetrax and the Mechamorph were transported into the Omnitrix itself. 
Inside, Ben and the Mechamorph continued to battle before being attacked by a swarm of Stinkflies just as Gwen and Tetrax were ambushed by a herd of Wildmutts. The four caught up with each other and they realized that the evil Way Big was inside with them just as he resurfaced. The Mechamorph, who was revealed to be Azmuth's father, attacked the Way Big in revenge for killing his son while Gwen explained 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 used Azmuth's father to reverse transportation and return them to Earth. Unfortunately, the Omnitrix malfunctioned again and transformed Ben's parents into Wildmutt and Heatblast, causing Gwen to realize that the evil Way Big was Azmuth himself. Leaving Max and Tetrax to handle his parents, Ben and Gwen followed Azmuth's father and Azmuth to the city park where Ben transformed into Way Big to subdue Azmuth and hold off his father while he and Gwen tried to reverse the transformation. They soon convinced Azmuth's father that his son was the very alien that they were fighting and the three worked 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 reprimanded Ben and Gwen for their errors and revealed his father is a Galvan wielding a Mechamorph-type armor. 
Returning to Ben's house, Azmuth transformed Ben's parents back into 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, told him to enjoy his fishing trip with Max and Gwen. Ben declined, having learned to be more responsible, and stayed home to finish his history report for school. The movie ended with Ben, Gwen, and Max on another road trip where they encountered Dr. Animo again and the three prepared for another exciting battle.
thumb|Ben meeting his 16-year-old self
10-year-old Ben reappeared in the Ultimate Alien episode The Forge of Creation, having come sometime after summer vacation. He was even less well behaved compared to his character from the Original Series (who was already obnoxious and immature). When he was examining 16-year-old Ben's Ultimatrix, he called NRG and Brainstorm "lame", Goop "weak", and Humungousaur "okay" due to his big size and stature.
Ben had continued to use the Omnitrix to encounter and defeat different types of 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's actions would earn him a great fame among the Plumbers, with some even calling him a legend.Magister Labrid