Fontes T-canon (a série animada Clone War) as pintam como um grupo já existente de clones de elite servindo com o general Jedi Anakin Skywalker e Capitão Clone CT-7567 , apelidado de" Rex ".
Por causa das técnicas de liderança menos ortodoxas de Skywalker e da latitude operacional que ele deu aos soldados do 501º, eles conseguiram completar missões extraordinárias sob circunstâncias difíceis, estabelecendo-se como um time de crack.
Among the 501st's earliest battles was the Battle of Christophsis, where they served under Skywalker, Captain Rex, and High Jedi General Obi-Wan Kenobi. Based out of Crystal City, the 501st troops managed to recapture Christophsis from the Confederacy, beating back Separatist General Whorm Loathsom's multiple assaults. However, Loathsom soon deployed a deflector shield to protect his battle droid troops, and the clone troopers were forced to pull back and defend the Republic's heavy cannons. After Skywalker and his newly assigned Padawan, Ahsoka Tano, destroyed the shield generator, the heavy cannons annihilated the droids and forced the Separatists to surrender. -- Wookiepedia > 501st Legion