Appo was a Clone Commander who served within the 501st Legion during the Clone Wars. He later served the Galactic Empire following the activation of Order 66, leading the 501st into battle against the Jedi Order.
During Order 66 Appo was among the 501st Clone Troopers that stormed the Jedi Temple on Coruscant and he met with Bail Organa when the Senator arrived. Zett Jukassa tried to make it to Bail's speeder when the clones started shooting at the Jedi Padawan. Zett was unable to make it but wounded many clones including Appo before getting shot dead.