CT-7567, nicknamed "Rex," was a clone trooper captain during the Clone Wars, the galaxy-wide conflict between the Galactic Republic and the Confederacy of Independent Systems. Rex was in command of Torrent Company, a unit of the famed 501st Legion in the Grand Army of the Republic. Rex served under Jedi General Anakin Skywalker, and was a freethinking, tough, and aggressive trooper. Though loyal and committed to his duty and to his fellow clones, Rex proved capable of questioning his superiors and, under extreme circumstances, outright disobeying orders if he believed them to be wrong. Rex displayed a strong working relationship and a degree of friendship with Commander Cody.
Under General Skywalker, Rex would go to many different planets throughout the galaxy. Rex assisted High General Obi-Wan Kenobi and General Skywalker during the Battle of Christophsis, when he worked with Commander Cody to root out a traitor, and later led Torrent Company during Confederacy General Whorm Loathsom's multiple counterattacks. Rex also met Skywalker's new Padawan, Ahsoka Tano, after she arrived on Christophsis. Rex also participated in the Battle of Teth, where he was one of the few clone survivors before reinforcements arrived. During inspections of Republic listening posts, Rex and Cody encountered a squad of droids on the Rishi moon, and led a group of rookie clone troopers to retake the base.
Rex participated in the Battle of Bothawui, and later assisted Skywalker and Tano during a mission to destroy a Confederacy listening post—and was one of the few clone troopers, along with Sergeant Denal, to survive the mission. After rescuing Jedi General Aayla Secura from defeat by the Confederacy with Skywalker and Tano, the Jedi and clones, including Rex and Commander Bly, crash-landed on the remote world Maridun, and Rex stayed with Anakin since he was injured, while the others found help. After Confederacy General Lok Durd arrived on the planet to test a new weapon, Rex and Bly helped to defeat the Confederacy and save the inhabitants of the planet. Rex would later be an asset during a short war on Orto Plutonia, and would also help halt the release of the deadly Blue Shadow Virus. Rex also helped Skywalker and Tano during the Battle of Ryloth and retrieving a stolen Jedi holocron.