Mermaid Man and Barnacle Boy are a duo of semi-retired superheroes from Bikini Bottom. They have been famous throughout the years and once considered retirement, but thanks to Spongebob SquarePants and Patrick Star, they've gotten out of retirement and ressumed being superheroes, despite their elderly ages.
Mermaid Man is the shorter obese one who's been used to the superhero ways and knows what it takes. Despite this, Mermaid Man goes insane when someone says the word "evil." He doesn't like evil.
Barnacle Boy is the taller one who is more cranky and uncooperative. More often then not, he gets annoyed by Mermaid Man, but the two are inseperable and seen together all the time.
- Mermaid Man is voiced by the late Ernest Borgnine and Barnacle Boy is voiced by Tim Conway.
- In The FT Squad's Adventures Series, Mermaid Man and Barnacle Boy will meet the FT Squad in The FT Squad's Adventures with Spongebob SquarePants and after The FT Squad Goes Finding Nemo, will join them in their adventures.