The original pilot for Invader Zim featured legendary actor Mark Hamill provide the lead voice. Debuting on Nickelodeon in 2001, Invader Zim creator Jhonen Vasquez managed to launch a character that is still relevant today. Despite being canceled after just two seasons, the series has continued to find new life through various formats, such as the recent Invader Zim: Enter the Florpus movie on Netflix.
Following the antagonistic alien, Invader Zim was created to target an older demographic for the studio and had a surprisingly quick development process. Nickelodeon contacts Vasquez based on some of his comic books and he quickly came up with the idea for Invader Zim. Once Nickelodeon heard the pitch for the pilot and ordered Invader Zim to series, it then came time for Vasquez to figure out who would voice his lead character. Fans of the character may associate Richard Steven Horvitz with the role, but it was the man behind Luke Skywalker who was originally going to supply the voice.
Mark Hamill's casting came during Vasquez' initial search for the voice of Zim. When he started this search, Vasquez wanted to find someone with a distinct voice so that the actor didn't have to do a weird voice every time. This led him to Hamill - who has a prolific voice career - and he cast him in the role. Hamill recorded his part for the original pilot, but Vasquez decided late in the process that Hamill's voice was not working with Zim and they went their separate ways. For more examples of how animated shows could've been very different, check out the latest Screen Rant video.
Despite having an entire pilot with Hamill's voice recorded, the audio of Hamill's take on the character has never been released. Considering Vasquez's preference to just let the natural voice of whoever he cast be how Zim sounds, then it isn't difficult to imagine what Hamill would bring to the role. If it would've stuck, Invader Zim could've been another notch in his voice acting work, which includes one of his most well-known roles as Joker.
Once Invader Zim and Vasquez did move on from Hamill as the voice of the titular character though, it wasn't the last time that the voice was changed. Vazquez's first choice to take over the part was Billy West and he did so in the pilot that aired. But, West was replaced with Richard Steven Horvitz once the how was given a full-season order. One of the reasons for this was West's involvement with Futurama, as he voiced the lead character, Phillip J. Fry. Due to his prominent role in that series, Vasquez did not want Zim to have the same voice as another current animated character.