Four Arms is a humanoid alien that is approximately 12 feet tall, has well developed muscles, two pairs of four-fingered arms and red skin. The black stubble stripe goes from the bridge of his nose to his neck. A second black stripe goes from his chin to his lower lip, and he has four eyes: a main pair and a smaller pair below them.
In the original series, Four Arms wears a white t-shirt with a black line going down it, black pants and fingerless gloves. He wears the Omnitrix symbol on his upper left shoulder.
Gwen as Four Arms has her pants, her chest is light blue, her arms, neck and back are dark blue. Her skin is darker red and she has Gwen's hair. She bears the Omnitrix symbol on her upper left shoulder.
In Ben 10-Generator Rex: Heroes United, Four Arms, in addition to his clothes in Ultimate Alien, he now also has his pants, fingerless gloves, and tattoo like stripes on his body, which are the same as the stripes of his shirt in Original Series, giving him the look of Four Arms in the original series.
In Omniverse, Four Arms now has 3 short spikes on the top of his head, a mustache, the black stripe on the top of his head is gone, he has no hair, he has a black tank top like shirt as a muscle man at a circus would have with one large green stripe, and black pants. He has a belt similar to Kickin Hawk's, Diamondhead's, Gravattack's and Shocksquatch's. He also has fingerless gloves with green cuffs at the wrist of his gloves. The Omnitrix is now on his belt instead of his chest.
11-year-old Four Arms in Omniverse looks the same as the original series but now has green eyes and the Omnitrix symbol on his shoulder is now green. Four Arms is so strong that he can create shock-waves simply by pounding his fists or clapping all four of his hands together, dubbed the "Big Smack".
In Protector of Earth, Four Arms can spin around while punching enemies around him and make a tombstone-like boulder by stomping. Four Arms' leg strength allows him to jump across entire city blocks in a single bound.
Sometimes Four Arms' bulk is a disadvantage; all the extra muscle mass makes him relatively slow, and his size, likewise, makes using things designed for smaller species difficult. When under the effects of a cold, Four Arms' strength and stamina are weakened, he develops pungent hives in his armpits, and his skin color turns a darker shade of red.
Ben 10 is an acclaimed American media franchise created by "Man of Action", and produced by Cartoon Network Studios. The franchise is about a boy who acquires a watch-like alien device called the Omnitrix attached to his wrist that allows him to turn into alien creatures.