Hamill confirmed the news on Twitter, which includes a first look at art of the character, Kavaxas, Demodragon of the Underworld.
"1st look at my #TMNT character. Based on his looks, think there's any chance he's a good guy? #villaintypecasting," Hamill teased.
Hamill is providing the voice for Kavaxas in the episode "Scroll of the Demodragon" in Season 5.