He has nearly impenetrable gray armor, a black helmet with a small, green triangle (presumably for sight) on it, and carries a large rifle. His Petrosapien physiology can manifest through the armor, allowing him to use his powers without removing it.
Unlike the other hunters, Tetrax is allied against Vilgax. Upon first discovering that Ben has the Omnitrix, he laments the fact that out of the planet's six billion inhabitants it would end up on the wrist of a child. He also berates Ben's lack of strategy in regards to its use. After helping Ben to defeat the other hunters, during which Ben learns to use the Omnitrix strategically, he decides that the Omnitrix is in good hands, allowing it to remain with Ben. He also gives Ben his hoverboard, saying that it might come in handy. Ben uses it several times throughout the series. In Ben 10: Secret of The Omnitrix, the hoverboard is melted in a vat of nuclear waste, but Ben is given a replacement.
Ben 10: Secret of the OmmitrixEdit
Tetrax returns in Ben 10: Secret of The Omnitrix, where his past is explained. As a being who cared about no one but himself, he became a mercenary and ended up hiring himself to Vilgax. When he finished the job Vilgax gave him, Vilgax created a weapon (using the crystal Tetrax stole) and used it to destroy Tetrax's home planet, Petropia when they would not bow down to him. This caused Tetrax to betray his former employer, and he now works as the Omnitrix Guardian and to rid the galaxy of evil. He arrives on Earth after receiving the Omnitrix's SDM (Self Destruct Mode) signal, and takes Ben aboard his ship in search of Azmuth, the creator of the Omnitrix and the only one who can deactivate the self destruct function. Unfortunately, Tetrax's problems are multiplied when Gwen stows away aboard his ship, and Ben's transformations are revealed to accelerate the countdown. On Incarcecon, Tetrax runs into Sixsix, another of the bounty hunters hired by Vilgax who ended up on Incarecon. After a brief battle, he and the Tennysons find Myaxx, Azmuth's former assistant. Because of her, Tetrax is forced to reveal that the Omnitrix's explosion will create an energy ripple that will destroy the entire universe. Tetrax then leads the group to Azmuth's compound on Xenon, where he faces Sixsix again before defeating him by delivering a punch to his head.
Tetrax returns in The Secret of Chromastone when he comes to Earth demanding that Ben hand over Chromastone. He forces Ben to transform into Diamondhead, thinking he'd transform into Chromastone, then uses a sonic device to shatter Diamondhead seemingly releasing Chromastone from the Omnitrix leaving Diamondhead alive in pieces. Tetrax gives Chromastone a crystal which it absorbs, then flies off into space. Tetrax reveals that Chromastone is the only one who can restore Petropia and its people back to life. He explains that the crystal he stole and gave to Vilgax (who used it to power the weapon that destroyed Petropia) was in fact a crystalized back-up for both his planet and its people. Upon discovering this Tetrax stole the crystal back from Vilgax and gave it to the freed Chromastone so it could use it to restore Petropia. This was Tetrax's way of atonement for his part in Petropia's destruction. However, his theft of the crystal didn't go unnoticed by Vilgax who followed Tetrax to Earth, demanding he hand over the crystal. Tetrax, Ben, Kevin, and Gwen are then chased by Vilgax who he believes are in possession of the crystal. Vilgax eventually manages to catch Tetrax demanding he hand over the crystal, but Kevin accidentally reveals the crystals location. Vilgax flies off to Chromastone's location to discover the newly restored Petropia (Ben and company race to stop him aboard Tetrax's ship). Angered that someone would use "his crystal" to restore a dead world Vilgax beats Chromastone who pleads for mercy, only to find Vilgax has none to give. Tetrax, Ben, Kevin, and Gwen arrive to see Vilgax beating Chromastone. Tetrax attacks Vilgax, but Vilgax shield protects him from the crystal projectiles. To Tetrax horror, Vilgax removes the crystal from Chromastone (before he can revive the planet's people). However Vilgax discovers the crystal power is gone (thus it is no longer useful to him) and flies off in disappointment leaving behind the dying Chromastone. All hope seems lost, but the dying Chromastone generates a new backup crystal and hands it to Ben before fading away. Unsure of how to use the crystal Ben transforms into Diamondhead (who instinctively knows how to use it). Diamondhead uses the crystal to restore the Petrosapiens to life. Tetrax and a revived Chromastone (who is revealed to be Sugilite) thank Ben for his help.
Tetrax is a bounty hunter with a strong desire to do what is right. This is partly due to his involvement in the destruction of his home planet, Petropia. Tetrax claims that he used to be a being who cared about no one but himself and that is what lead him to become a mercenary. It is only after Vilgax destroyed his home that he realized the effect his actions had on his own people. That experience made Tetrax into the heroic Omnitrix Guardian he became. He helps Ben become a better hero, teaching him to use the Omnitrix wisely (Ben later repays him by reviving Petropia's people). He also deeply despises Vilgax due to their history.
Being a Petrosapien, Tetrax possesses abilities same as Diamondhead's: his body is made of organic, nearly indestructible, diamond-like crystals who can refract light, causing him to be immune to most laser and energy weapon. He has a limited ability to regrow lost limbs, as well as alter his own physical constitution, making him able to do things such as fire crystal fragment as projectiles, turn his hands into blades, create structures of this crystals, etc. In addition to his natural powers, Tetrax is also equipped with various devices and weapons, such as an hoverboard, his own personal ship.