BioEditChopper is/was a Standard Phase 1 Clone Trooper who was assigned to Slick's Squad in the 212th Attack Battalion, who was the main witness for discovering the truth about Sgt. Slick being a traitor to the Republic.
Chopper served as an engineer for Slick's Squad, and often liked to collect battle droid fingers and other parts to collect as trophies for every battle he fought in which involved droids.
Chopper is/was often very sensitive, serious, and often laid-back and good-humored about certain moments in certain missions and battles. Hence, him being very serious and some-what scheming around Slick during the interrogation on Christophsis.
Chopper was also accused of being a Seperatist spy, yet Slick actually was, hence Slick retreating after Chopper blew his cover, as well as attacking Chopper.
Chopper wears Standard Phase 1 Clone Trooper armor, while his facial appearance consists of having shaved hair, with a discolored eye, and severe facial scarring on the left side of his face (similar to Commander Wolffe.)
Chopper is one of the more well-known Clones in Slick's Squad.
He is one of the only Clone Troopers to have a discolored eye and severe scarring on one side of their face.
He is also considered to be one of the most unique Standard Clone Troopers.
Star Wars: The Clone Wars "Hidden Enemy"
Star Wars: The Clone Wars Character Encyclopedia
Star Wars: The Clone Wars "Shadowed" web-comic