TJ-55 was a T-series military strategic analysis and tactics droid commanding a Separatist Droid Army infantry detachment in the Battle of Christophsis during the Clone Wars. This droid led a complete battalion of B1-series battle droids in the conflict, participating in a surprise attack against dug-in Republic forces based on intelligence received from a traitor among the clone troopers. Despite the obvious betrayal, the Republic soldiers sought answers even as they fell back before TJ-55's troops. As a gunship came to rescue the remaining soldiers, the clone trooper Gus severed TJ-55's head, hoping to use the information stored in its memory to unmask the traitor. Subsequently, Clone Captain Rex and Clone Commander Cody examined the head and uncovered the presence of a traitor within their ranks, discovering that a signal had been sent to the Separatists from a terminal in the barracks used by Sergeant Slick's men.