Fourarms is about a 12-foot tall alien with four muscular arms and four eyes.
The Omnitrix symbol is on the upper left shoulder and in Ultimate Alien the Ultimatrix is on his chest.
In the Original Series, The black stubble stripe goes from the bridge of his nose to his neck. A second black stripe goes from his chin to his lower lip, and he has four eyes: a main pair, and a smaller pair below them.
In Ultimate Alien, since Ben lost the feature to cloth his aliens, Four Arms is now armored with a gold belt, gold leggings, and 4 golden shackles on every arm.