Ben Tennyson

Benjamin Kirby "Ben" Tennyson was a normal ten-year-old kid until he found the Omnitrix, a powerful watch-like device that allowed him to turn into ten different aliens. Though initially immature and clumsy, Ben grew to be a true hero. By the time he was sixteen, he had become famous in not only his hometown of Bellwood, but on Earth and beyond. Ben has also been deputized by the Plumbers and gained more aliens as time progressed.

Appearance
Ben's physical appearance has changed throughout the series from a ten-year-old to a sixteen-year-old. However, he retains some recurring characteristics. He has shaggy brown hair, green eyes, pale skin, and he's quite skinny for his age, though he shows a lot of muscle definition due to being athletic.

When he was 5, as revealed in a flashback of how he first met his future frenemy Mr. Baumann, Ben wore green overalls with a white shirt underneath it. White numbers saying "5 1/2" where on a black square in front of his overalls.

In the original series and Omniverse flashbacks, Ben's usual clothes consists of a black-striped, white shirt with short sleeves, military green cargo pants and black and white sneakers with black stripes. Ben wears the prototype Omnitrix on his left wrist.

In Alien Force and Ultimate Alien, Ben wears a black shirt, blue pants and a green jacket with white stripes and the number 10 on it, and black shoes. Ben wears the prototype Omnitrix in Alien Force and the Ultimatrix in Ultimate Alien on his left wrist.

In Omniverse, Ben wears a black shirt that has a green stripe in the middle with a white 10 and green stripes on the sides of his shirt. He wears brown cargo pants with pockets at the knees and green and white shoes. He later gains a white hooded jacket with green stripes on both arms and a green number 10 on the right side. He wears the Omnitrix on his left wrist.

Personality
Initially cocky, childish and arrogant, Ben's immaturity and attention-seeking behavior often led him to joke around, regardless of the situation. His allies often criticized his attitude, unaware of the fact that he used humor to mask his fears. Despite some childish attitude, he was heroic, caring and generally good-natured, always willing to save others at any time.

Over the years, Ben has displayed good leadership skills, as well as the ability to adapt his attitude to a situation, becoming serious when it's called for. He became more mature, responsible and sensible. He's kind-hearted, willing to sacrifice even his own life for others. His idealistic views and unwillingness to compromise his values – aspects condemned by Azmuth, yet commended by others – sometimes drive him to act against reason, such as helping his enemies if they need it (most remarkably Vilgax). Professor Paradox has praised Ben's good nature, going so far as to say he had the gift to make the right choices at the right moments.

However, when Ben fails to save someone, or if someone gets hurt because of his failures, he becomes angry and much more violent. Perhaps the most notable of these instances is when Kevin willingly mutated himself to succeed where Ben had failed and stop Aggregor, Ben was set on killing Kevin, even fighting Gwen when she refused to help him. He also threatened to hunt down and destroy the Forever Knights once The Purge making Driscoll promise to cease the hunting of aliens.

Though often stated to be silly or unintelligent because of his immaturity, Ben is cunning and resourceful when needed, quickly adapting when the Omnitrix doesn't provide him with the alien he wanted.

Later on, Ben starts thinking of himself as more of a superhero than a Plumber, often remarking that he's not a cop, but a superhero. Although he once again became cocky, he retained his selfless and heroic nature.