BioEditGus is/was a Standard Phase 1 Clone Trooper for Battalion Sergeant Slick's squad in the 212th Attack Battalion, who was one of the interrogators who questioned Slick for being a traitor.
Gus was a clone trooper for sergeant Slick's platoon (to whom the platoon was unnamed), who was known for using and calibrating stationary weapones like cannons and heavy turrets, as well as assisting Jedi General Obi-Wan Kenobi and Commander Cody with weapon operations with Jedi General Anakin Skywalker an Captain Rex.
He eventually witnessed a traitor amongst the Republic, but originally assumed that it was his loyal partner Chopper. But Sgt. Slick eventually revealed himself as the traitor after attacking Captain Rex, Commander Cody, and Chopper.
Both him and the other members of his squad eventually were killed towards the end of the Clone Wars Era.
Gus wears Standard Phase 1 armor, while his facial appearance consists of being bald with a unique "double-stash" style of facial hair. (To distinguish himself from the other Standard Clone Troopers.)
Gus is one of the very first and only Clone Troopers to have a "double-stash" style of facial hair.
Him and Chopper are the two most well-known members of Slick's squad. (Aside from their leader, of course.)
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Star Wars: The Clone Wars Character Encyclopedia
Star Wars: The Clone Wars "Shadowed" web-comic