sentences:  Mark Hamill was originally hired to do the voice of Zim for the pilot episode, but was replaced before the pilot was shown to Nickelodeon executives because Vasquez felt his voice did not feel right for the character.Hamill was replaced by voice acting professional Billy West, who remained the voice of Zim for the pilot.After the show was picked up for a full series, Vasquez decided to replace West with Richard Steven Horvitz, saying that West was "too well known" and that he wanted all of the voices for the main characters to be unique and not voices people had heard before.