Diamondhead is the Omnitrix's DNA sample of a Petrosapien[6][7] from the planet Petropia.[8][9]

Being a silicon-based life form,[10][9] Diamondhead's body is composed entirely of aquamarine crystals, which are of a very tough and durable diamond-like substance.[MW 1] He sports four crystal shards on his back and has a sharp head.

In the Original Series, Diamondhead had yellow eyes and wore a sleeveless uniform that was black on the right half and white on the left with a black patch on the left shoulder where the original Omnitrix symbol was.

In Back With a Vengeance, Diamondhead wore a yellow raincoat.

In Destroy All Aliens, Diamondhead looked the same as in the Original Series, except his eyes had jewel-like facets and his outfit had detailed textures.

In Race Against Time, Diamondhead's skin was semi-translucent. His skin was a darker shade of green while his bodysuit is more metallic with some patterns of spandex.

In Alien Force and Ultimate Alien, Diamondhead's lower body, torso, and the top of his head were similar to Chromastone's, consisting of an indigo rock which has black lines and dots over it. There were six crystal shards on his back instead of four and he also sported two more on the front of his chest. His eyes were green and he wore the original Omnitrix/Ultimatrix symbol on his chest. Gwen Prime as Diamondhead shared these exact same traits.

In Heroes United, Diamondhead had crystal blades on his forearms and his crystal skin looked more realistic due to being drawn in Generator Rex's art style. He also had a vertical black line in the middle of his face.

In Omniverse, Diamondhead has sleeveless clothing that is all black with one large green stripe down the middle up to his belt, and wears black pants. He has a green belt with white stripes on which he wears the Omnitrix symbol. Diamondhead no longer bears the crystals on his chest, and the crystals on his back have also grown in length. His jaw is larger, he wears black shoes that are green on the bottom, and there are now only two crystal shards on his back. His arms and shoulders also seem to have much more girth.

11-year-old Diamondhead looks almost the same as in the Original Series, but the left side of his suit is missing the black patch around the Omnitrix symbol and the crystals on his back, as well as his jaw, are bigger. His eyes are green and the Omnitrix is recolored.