The ninth season of the American animated television series SpongeBob SquarePants, created by animator and former marine biologist Stephen Hillenburg, originally aired on Nickelodeon in the United States from July 21, 2012, to February 20, 2017, and contained 26 half-hour episodes. The series chronicles the exploits and adventures of the title character and his various friends in the fictional underwater city of Bikini Bottom. The season was executive produced by series creator Hillenburg and writer Paul Tibbitt, the latter of whom also acted as the showrunner for the first 11 episodes of the season. Starting with "Lost in Bikini Bottom", Marc Ceccarelli and Vincent Waller became the supervising producers and showrunners and served in that position for the rest of the season.

Mermaid Man and Barnacle Boy are a duo of fictional characters from the American animated television series, SpongeBob SquarePants. They were respectively voiced by guest stars Ernest Borgnine and Tim Conway, who both previously starred in the 1960s sitcom McHale's Navy. Mermaid Man and Barnacle Boy first appeared in the eponymous season one episode that premiered on August 21, 1999, and have since been featured as recurring characters. Following the actors' deaths, the characters have been relegated to non-speaking cameos after creator Stephen Hillenburg requested not to recast the characters.