Not to be confused with his father Pistar.
Piestar is a minor character in Redtail's Awesomeness. He gives Redstar all nine of his lives since the rest of StarClan were vacationing in the bahamas. He also tells Redstar that it is possible for him to grow older and eventually die because of it, adding that he should journey to the Tribe of Endless Eating and become immortal.
In The Forgotten Warrior, he returned as a more important character. When Hollyleaf returned, he attacked her but was knocked away by her. She then tried to eat him, but Jayfeather stuffed Hollyleaf full of deathberries. After Hollyleaf died, Ivypool asked Piestar if he wanted to join them for a feast. Everyone was eating pie, so Piestar freaked out and tried to kill them for enslaving his brothers. He then revealed himself as the Dark Forest leader and murdered Brambleclaw. Later, he told Blossomfall to disguise herself as Cinderheart and seduce Lionblaze. She agreed. Later, Piestar told Hawkfrost to blow up the world. Hawkfrost turned into a she-cat and ran away. The book ended with him firing a pie into the sky, causing World Domination to appear.