Four Arms

Fourarms is a tetramand (pronounced Tet-Rah-man-d) from Khoros (Khor-ose). It is the sixth alien to appear on the series. It was also Ben's most used alien form when he was his younger self, since that was Ben's favorite fighting style back then.

Abilities
Possessing four arms, four eyes, armor-plated skin, and extremely dense musculature, Fourarms is rarely matched in raw strength. His strength is such that he can create shockwaves simply by smashing the ground or clapping all four hands together, dubbed the "Big Smack". Fourarms' muscular legs also allow him to leap several city blocks at a time.

As a child, Fourarms had hardly any muscles but only a large head.

Weaknesses
Sometimes Fourarms' bulk is a disadvantage,since for it he is also not able to run very fast. Fourarms' massiveness makes him unable to hide anywhere or sneak behind anyone. He has been known to scare some people without meaning to and villains can get a hold of his leg easily because he is slow.

When Ben had a cold, Fourarms turned orange and had stinky hives. Strangely, when Ben tries to change into Fourarms, the Omnitrix seems to nearly always change into a different alien. This may be the AI of the Omnitrix which uses more strategy than Ben who simply likes smashing people.

Planet
Tetramands are giants compared to most species, standing ten feet on average. The harsh wasteland of their home planet, Khoros, has turned the Tetramand race into physical powerhouses, a trait carried over to Fourarms.

Future
In the future when Ben becomes Ben 10,000 a pop-up in the Ben 10 Enhanced marathon reinforces this, stating that "Ben's aliens look different because they are no longer 10".

Future Fourarms now has a short-sleeved shirt, which moved the Omnitrix symbol to the center of his chest. It also displays jagged spikes on the shoulders and arms along with two sharp fangs on the bottom corners of his mouth. In the future, his black pants completely covers his feet. A different Tetramand appears in the same appearance in Ben 10: Alien Force.