Captain Rex belonged to helped Anakin Skywalker lead his battalion of clones because Annie himself was often too busy dreaming about Padme and abusing his padawan. Captain Rex failed because he got distracted by Ahsoka Tano too often and often had hot, underage, interspecies relations with her and Cody. The other clones reported this so they could have Ahsoka and Cody to themselves to bring Rex to justice. Mad, Rex led them on a mission that meant sure death and one of the coolest clones (Heavy) was killed. Rex fought in the rest of the war and was very depressed when the emo killed Ahsoka. But Cody cheered him up. Hard.