SpongeBob SquarePants is the title character of the series of the same title. He has appeared in every episode of the series and obviously has the most appearances of any other character.
Although SpongeBob has appeared in every full-length episode of the series, he does not appear from several shorts. These include the What If SpongeBob Was Gone? shorts, Friend or Foe shorts, and the Merry Nickmas shorts Patrick the Snowman, Plankton's Holiday Hits, and A Chuckie Finster Christmas, Channukah, Kwaanza, Winter Solstice. Although, he has appeared in many other shorts.
He played a major role in all episodes, except the episode in which he plays a minor role or made a cameo, as well as Tea at the Treedome, Mermaid Man and Barnacle Boy, Sandys Rocket, Squidward the Unfriendly Ghost, I Was a Teenage Gary, Arrgh!, Texas, Rise And Shine, Ugh, ...This list is incomplete, but you can help SpongeBob SquarePants by expanding it.
The Primary Universe SpongeBob does not appear in the episode The Algae's Always Greener