Mermaid Man and Barnacle Boy are fictional characters in the Nickelodeon animated television series SpongeBob SquarePants. Mermaid Man was voiced by Ernest Borgnine from 1999 to his death in 2012, and Barnacle Boy is voiced by Tim Conway. Mermaid Man and Barnacle Boy were created and designed by Stephen Hillenburg. The characters debuted on August 21, 1999 in the series' episode "Mermaid Man and Barnacle Boy".