Diamondhead

Diamondhead is the Codon Stream's DNA sample of the Petrosapien species from the planet Petropia. Ben first transforms into Diamondhead in "And Then There Were 10" when he needed to fight Vilgax's giant robot.

History
Diamondhead was voiced by Jim Ward in the first series, Daran Norris in the live-action movie, and Dee Bradley Baker in the second series.

Diamondhead makes an appearance in the third season premiere of 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. In this series, his crystals can explode and he demonstrates the ability to psychokinetically control the crystal he creates.

Abilities
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.

Planet
Petropia' is a crystal-covered world, and its inhabitants are silicon-based lifeforms. The majority of its inhabitants live in underground kingdoms. The planet was destroyed by Vilgax with some assistance from a Petrosapien named Tetrax Shard who unknowingly helped Vilgax destroy his home planet. As of "The Secret of Chromastone", Petropia and all of its inhabitants have been restored through the Crystalsapien Suglite, the Guardian of Petropia.

Ben 10: Alien Force
Diamondhead's body is different in that his Omnitrix symbol is now in his chest and his eyes are now green. He also has a similar body structure to the one of Chromastone, a related species. In the episode "The Secret of Chromastone" it is revealed that all Petrosapiens have a dark purple body (in the original series we never saw that because both Ben, Tetrax and all the Petrosapiens were wearing clothes). Ben transforms into Diamondhead after Vilgax destroys Chromastone's body (seemingly killing Ben in the process, but the crystals that made up Chromastone re-constituded into Diamondhead, giving Ben access to this form once again. As Diamondhead, Ben states "You're in trouble Vilgax, I've had a lot of pratice with this one.", indicating Diamondhead is one of the alien forms that he had a lot of experience with (this maybe in reference to a scene from an episode of the original series, in which a young Ben can be seen training in this form under the guidance of Grandpa Max), possibly due to it being one of his original 10 alien forms. Ben proves this by using it to literally crushing Vilgax (under three giant chunks of crystal), forcing the villian to yield defeat. Ben's use of Diamondhead to defeat Vilgax is both ironic & fitting given that Vilgax is the one ultimately responsible for the destruction of Petropia.

Diamondhead is now once again selectable in the Omnitrix. Ben briefly transforms into Diamondhead in the episode "Single-Handed" after becoming trapped in the Null-Void after he is dimensionally displaced from his left hand (the hand that wears the Omnitrix) by the bounty hunter Sunder. This saves Ben's girlfriend Julie Yamamoto from Sunder, while she is trying to protect Ben's left-hand & Omnitrix. Ben's dimensionally displaced hand protects Julie by firing Diamondhead's crystal shards. However, this causes problems for Diamondhead, as his left arm also fires shards, unintentionally destroying a rock bridge he was walking on. Diamondhead also appeared in the episode "In Charm's Way", fighting a hypnotized Kevin.

Trivia

 * In the German version of the series, Diamondhead - like so many others of Ben's aliens - was for unknown reasons misnamed. In his case he was called "Stahlschädel" ("Steel Skull"), even though he is evidently composed of a crystalline substance.