CT-7567 was a veteran clone trooper captain who led the Grand Army of the Republic's acclaimed 501st Legion during the Clone Wars. Bred and trained on Kamino, 7567 entered into Republic service at the Battle of Geonosis in 22 BBY. He gained respect as an honorable commander from Jedi officers and clone troopers alike, becoming known as one of the best and toughest clone troopers in the Grand Army. 7567 was even selected for special command training under Advanced Recon Commando Alpha-17, following which he took the nickname "Rex." As the captain of the 501st, Rex served as second-in-command to Jedi General Anakin Skywalker, whose bravery and unorthodoxy in battle he came to share. He was close friends with Marshal Commander Cody, with their relationship mirroring that of their respective Jedi Generals, Skywalker and Obi-Wan Kenobi. The four of them often received joint assignments to coordinate front-line campaigns against the Confederacy of Independent Systems.