When 10-year-old Ben Tennyson discovers a mysterious watch, he gains the power to transform into a number of different aliens, each with awesome powers. Ben realises that he must use these powers to help others and stop evildoers, but that doesn't mean he's above a little super powered mischief now and then.
Ben Tennyson might seem like an ordinary 10-year-old boy — he plays video games, rides his bike and is a bit of a trouble maker - but thanks to his Omnitrix watch, he also has the ability to change into 10 different alien heroes.
Diamondhead is a crystalline alien whose body is harder than diamond. Out of all the Ben 10 aliens he's the most invulnerable to physical attacks, and can cut and slash through almost anything. He can also use his body to reflect light and beam-based weapons.
Whenever Ben needs to smash, throw or beat something up, Fourarms is the hero of choice. Standing twelve feet tall, this formidable four-armed Ben 10 alien uses his strength to dish out punishment, while his tough skin protects him from harm.
Ghostfreak is a shadowy one-eyed alien with ghost-like powers, able to pass through walls and turn invisible. His ghastly appearance is also good for putting fear into the hearts of criminals everywhere, as Ghostfreak is the creepiest of all of the Ben 10 aliens.
At a tiny five inches tall, Grey Matter is part of an frog-like alien race bred to enter complex machines and repair them from the inside. He gives Ben a temporary boost in intelligence when transformed, and his slimy skin makes him the hardest to catch out of all of the Ben 10 aliens.
Heatblast was the very first of the Ben 10 aliens to ever appear. He comes from an alien race that live on a sun rather than a planet, and he can project bolts of fire from his hands and mouth and make fireballs to throw.
The aquatic hero of the Ben 10 aliens, Ripjaws is an extraordinary swimmer. He can breathe underwater and change his legs into a large tail with fins, which means he's remarkably fast in the water. He can also unhinge his powerful jaws to deliver a devastating bite.
Stinkfly is a winged insectoid alien and expert flier. He can also take care of himself in a fight, using his pincers and sharp tail as impressive natural weapons. Unlike the other Ben 10 aliens, Stinkfly has a reputation for smelling bad - hence the name!
A living machine with liquid metal skin, Upgrade can reshape his body at will, and merge with any mechanical device from a blender to a satellite. He can then "upgrade" the device into something more advanced than any existing Earth technology.
Wildmutt is the most animal-like of the Ben 10 aliens, with superhuman athletic ability and heightened senses of smell, hearing and taste. He's a cross between a dog, a lion, a wolf and a gorilla, and he can also fire the quills from his back as projectile weapons.
XLR8 is one of the Ben 10 aliens with some unique tricks up his sleeve. He has lightning-quick reflexes and the ability to reach speeds in excess of 300 mph. He can run up sheer walls and across mud, ice and water, create tornadoes by running in a small circle, and he can quickly dodge attacks.