Diamondhead (voiced by Jim Ward on Ben, Charlie Schlatter on Kevin and Vanessa Marshall on Gwen in the first series, Daran Norris in the live-action movie and Dee Bradley Baker in the second series) is a Petrosapien ("Petro-" referring to rocks, "sapien" referring to an intelligent being; Petrosapien would mean "intelligent rock") from the planet Petropia (a combination of the Greek "Petro-" and "topos", forming a word similar to "rock place"). The planet was destroyed by Vilgax with assistance from Tetrax, who unknowingly helped him create the weapon that destroyed his home. Ben first transforms into Diamondhead in "And Then There Were 10" when he needed to destroy Vilgax's giant robot. In the planning stages, Diamondhead was set up to be one of the aliens Ben would have discovered later on, while Cannonbolt would have been one of the original ten. Diamondhead's body is composed of an extremely durable organic crystal, making him nearly invulnerable. Diamondhead can control his crystal physiology at will, allowing him to create crude crystal weapons from any part his body on demand or fire crystal shards from his hands. This same ability also allows him to regenerate to an extent, such as regrowing lost limbs. In addition to growing crystal from himself, Diamondhead can grow crystal over other objects. Lasers and other similar weapons are useless against Diamondhead, as his crystal body acts as a prism, refracting the beams. The one drawback to Diamondhead's crystal form is the crystal itself, which can shatter if exposed to sufficiently strong sonic vibrations. While Petrosapiens can regenerate limbs, there is a limit to how much damage they can recover from.
Diamondhead makes an appearance in the third season premiere of Ben 10 Alien Force, regenerating from Chromastone's remains after Vilgax destroyed him. Diamondhead's appearance is slightly altered, with a primarily dark blue uniform that also covers part of his head(mostlikely due to his forming from Chromastone). In this series, his crystals can explode and he demonstrates the ability topsychokinetically control the crystal he creates. He also has the ability to absorb energy due to the fact that he is part Chromastone.