BioEditSlick is/was an unmarked Battalion Sergeant for the 212th Attack Battalion, who led his own squad (to whom is unnamed), and eventually became a traitor to the Republic.
Slick began as a Standard Phase 1 Clone Trooper who was assigned to the 212th Attack Battalion and the 501st Torrent Co., but eventually was promoted to Battalion Sergeant for the 212th because of how brave he originally was being all-alone in the battlefield on Christophsis.
He was eventually captured by Sith Assassin Asajj Ventress during his "bravery" moment on Christophsis after he tried defeating her. She eventually decided to use him as a spy for the Seperatists by seducing him; thinking that the Jedi are using him and the other Clone Troopers as "pawns"; yet the battle droids are often used as pawns.
Slick eventually destoyed most of the Clones' reinforcements and infantry on Christophsis, as well as revealing himself in front of Captain Rex, Commander Cody, and his own squad who arrested him later-on.
He was supposedly executed in the Republic prison on Coruscant; yet this is unknown.
AppearanceEditSlick has Standard Phase 1 armor, while his facial appearance consists of having a unique "buzzed-fade" haircut modified from the standard "high-fade" haircut that most Clone Troopers (including Jango Fett) have.
Slick originally was meant to have unique orange-colored markings for the 212th Attack Battalion, but since he decided to join the Seperatists, he didn't really care.
He originally was meant to have red-colored hair, but the producers decided to have him blend-in with the other Clones.
Slick is one of the only Clones to betray the Republic.
He is also one of the only unmarked officers.
For being a lesser-known character, there is a lot of information known about Slick.
Slick's name ironically suits him well, since he sneaks around very "slick".Battalion Corporal Crys for the 212th Attack Battalion actually replaced him.
Star Wars: The Clone Wars "Hidden Enemy" (First Appearance)
Star Wars: The Clone Wars "Shocked" web-comic