TJ-55 was a T-series military strategic analysis and tactics droid who led an infantry detachment from the Separatist Droid Army during the Battle of Christophsis of the Clone Wars. This unit led a full battalion of B1-series battle droids during the battle, which participated in an ambush against entrenched Republic forces on the basis of information provided by a traitor in the ranks of the clone troopers. A betrayal obvious to them, the Republic forces sought answers even as they retreated in the face of TJ-55's troops. As a gunship arrived to retrieve the survivors, the clone trooper Gus decapitated TJ-55, hoping to use the data contained within their memory to expose the traitor. Clone Captain Rex and Clone Commander Cody would later analyze the head and discover that there was a traitor in their ranks, finding that a signal had been transmitted to the enemy from a terminal in the barracks for Sergeant Slick's men.