Rex, formerly designated CT-7567, was a veteran Clone Captain, Clone Commander, and Advanced Recon Commando who commanded the Grand Army of the Republic‘s famed 501st Legion of clone troopers during the Clone Wars. Rex later served as a captain and commander within the Alliance to Restore the Republic during the Galactic Civil War. Rex participated in many battles over the course of the Clone Wars. As the captain of the 501st, Rex served as second-in-command to Jedi General Anakin Skywalker, whose bravery and unconventionality in battle he came to share. In addition to being a close friend of Skywalker, he also became friends with Skywalker’s apprentice, Ahsoka Tano. He was close with Marshal Commander Cody, with their relationship mirroring that of their respective Jedi Generals, Skywalker and Obi-Wan Kenobi, whom Rex was also well acquainted with. Rex and his companions often worked together during the front-line campaigns against the Confederacy of Independent Systems.
Throughout his career, Rex proved to be an effective leader who truly cared for the men under his command, even as he began to doubt his own future—and those of his clone brethren— in the Republic. His leadership was put to the ultimate test at the Battle of Umbara, when he was forced to lead the 501st Legion under the obstinate and aggressive Jedi General Pong Krell, who was secretly a Separatist agent. Rex’s experiences with Krell forced him to reappraise his rigid adherence to orders— however, this had not been the first time Rex had questioned his purpose and orders. A notable example had been during the Battle of Saleucami, when he allowed the clone deserter Cut Lawquane to stay out of the war. Rex used his combat skills and training to help train local insurgents on Onderon to emancipate their world. Rex’s faith in the Republic was sorely tested by events such as the framing of Tano and the murder of his longtime comrade Fives, who had gone rogue after unearthing an anti-Jedi directive that had been bred into all the Republic’s clone troopers.
Fives’s death led him to uncover his inhibitor chip, which enabled him and his longtime friend Ahsoka to escape Order 66 after the Siege of Mandalore. After living on Seelos with fellow Clone Commanders Gregor and Wolffe, Rex joined the Phoenix Cell and reunited with his old friend Tano. Rex also became a reliable ally of the Spectres rebel cell and forged enduring friendships with the Great Jedi Purge survivor Kanan Jarrus and his apprentice Ezra Bridger as well as the rest of the Ghost crew. During the early stages of the Rebellion, Rex would use his skills and knowledge to help advance the Rebel Alliance’s cause. He was eventually promoted to the rank of commander and fought in the climactic Battle of Endor, which saw the first death of Emperor Palpatine, the redemption of his former Jedi General Anakin Skywalker, and the destruction of the second Death Star.