William E. Martin, also known as Bill Martin, was an American voice actor, musician, and screenwriter whose career spanned several decades until his passing in 2016. His first movie voice role was as the Rock Man in the 1971 animated film The Point. In addition to his work in animation, Martin co-wrote the screenplay for the 1987 film Harry and the Hendersons.

Martin is perhaps best recognized in animation for providing the voice of the villainous Nightmare King in the 1989 animated feature Little Nemo: Adventures in Slumberland, where he was credited as William E. Martin. This role placed him in a high-profile, internationally produced film that combined Japanese animation with an American voice cast. The Nightmare King is the tyrannical ruler of Nightmare Land and the main antagonist of the film, who is released from his imprisonment beneath Slumberland and later confronted by the young protagonist Nemo.

Beyond this film, Martin built a substantial career voicing characters in numerous iconic animated television series of the 1980s and 1990s. He is notably remembered for taking over the role of The Shredder in the original Teenage Mutant Ninja Turtles series following the departure of James Avery, voicing the character in seasons eight and ten. Other television voice credits include roles in The Transformers as Broadside, The Real Ghostbusters as Samhain, Challenge of the GoBots, and Karate Kommandos as Claw. Martin also appeared in a cameo role in the 1997 television movie Hey, Hey, It's the Monkees.

Martin passed away on January 27, 2016.