A clone trooper in Republic service, Appo took part in a number of critical battles during the fight against the Separatists. As a sergeant, he served under General Pong Krell on Umbara, and saw firsthand Krell’s willingness to throw away the lives of his troops. In the final days of the war Appo accompanied Anakin Skywalker to Coruscant’s Jedi Temple as part of Order 66. When Senator Bail Organa arrived during the aftermath of the Temple attack, Appo told him of the “Jedi rebellion” and ordered him to leave the area.