- Spongebill Squareshorts (voiced by Billy West)
- Proto Star (voiced by Bill Farmer) is SpongeBill’s Friend.
- Squidington Tenlegs (voiced by Dee Bradley Baker) is a squid with 8 hands who most of the time hates Spongebill, but deep down he’s just a loveable softie.
- Eistein Hermit Crabs (voiced by Jim Cummings) is Spongebill’s Boss.
- Silly Squirrel (voiced by Jennifer Love Hewitt) is Spongebill’s Girlfriend.
- Hitler B. Plankton (voiced by Jeff Bennett) is The Main Antagonist.
- Garlic the Snail (voiced by Frank Welker) is SpongeBill’s Pet.
- Mrs. Clouds (voiced by Tara Strong) is a fish with legs and Proto’s Girlfriend.
- Percy Crabs (voiced by Kath Soucie) is Eistein’s son.
- Carlton Plankton (voiced by Tress MacNeille) is Hitler’s Younger and Much Nicer Sister.
- Sodor Man (voiced by Jess Harnell) is the Star of Percy’s Favorite TV Show.
- Isle Boy (voiced by Rob Paulsen) is Sodor Man’s Assistant.
- Falling Chinaman (voiced by Neil Riley) is a Green Ghost who likes to Scare SpongeBill and Proto.
- Man Rock (voiced by Brad Garrett) is a Sarcastic Living Statue.
- Brown Bubble (voiced by R. Lee Ermey (1999-2014), Kevin Michael Richardson (2015-present)) is a Shark who leads an army.
- Lenny the Lobster (voiced by Maurice LaMarche (1999-2014), Fred Tatascoire (2015-present)) is a Lobster who is Spongebill’s Foreign Friend.
- Octington France (voiced by Jeff Bennett) is Squidington’s Brother who works at a Donut Shop That Proto Likes.
- Pom the Pirate (voiced by Jeff Bennett) is a Pirate who is the narrator and host of the show. He also sings the Theme Song. In one episode, he actually meets SpongeBill in real life.
- Paul the Parrot (voiced by Charles Nelson Reilly (1999-2006) and John DiMaggio (2009-present)) is Pom’s Parrot. When Pom is absent, Paul takes over to narrate the stories.
- King Uranus (voiced by Dom DeLuise (1999-2006) and Maurice LaMarche (2006-present)) is the King of the Mermaids
- Princess Mika (voiced by Lena Headey) is King Uranus’s daughter.
- Bubble Boss (voiced by Tom Kenny) is a Snobbish Pufferfish Who is Sometimes Hitler’s Helper.
- Stinky Spongeton (voiced by Clancy Brown) is Spongebill’s Cousin.
- James East (voiced by Rob Paulsen) is a Bank Robbing Sea Turtle.
- Miriam Hermit Crabs (voiced by Betty White) is Eistein’s Wife.
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