Butters has made very few appearances in some episodes. He only started to became a regular character upon Kenny's death in season 6. He has since been used almost as regularly as the main four boys. Butters is the character that the others usually make fun of. He is nervous, naive, easily manipulated, yet he remains very optimistic. He is often punished by his overbearing parents, and sometimes used by his peers for their own amusement. Butters always gets grounded. To further represent Butters' unluckiness, it is revealed in the episode "AWESOM-O" that his birthday is on September 11. Butters became important after he was the replacement for the semi-permanently dead Kenny in season 6. He also has an alter ego which he named "Professor Chaos". His character is based on animation director Eric Stough.