Plankton's cellmates are the secondary antagonists of the SpongeBob SquarePants episode Jailbreak! They are a group of prisoners who worship Plankton and help him break out of the Bikini Bottom Jail and steal the Krabby Patty secret formula.
The purple cellmate was voiced by Bill Faggerbakke, who is best known as the voice of Patrick Star and the whale cellmate was voiced by Mark Fite, while the other cellmates' voice actors are unknown.
They were taking food from Plankton, but they did not know who he was at the time. The light blue cellmate unknowingly tries to eat Plankton alive. Plankton yells at the light blue cellmate and tells him that he can't eat him and explains that he is the most evil genius in Bikini Bottom causing the purple cellmate, along with Reggie to get angry and then beat up the light blue cellmate because they thought he was calling himself Plankton. The purple cellmate mentioned that he and the other cellmates are big fans of Plankton because his chum is helpful for pulling off crimes.
After the light blue cellmate was beaten up, he spat Plankton out of his mouth and caused him to crash into a wall.
Plankton gets everyone settled down, and the cellmates agree to help Plankton escape from prison and steal the Krabby Patty secret formula. However, Plankton and his cellmates were later arrested and taken back to jail.
The whale cellmates is a sperm whale who has a scar on his face and he was used as a battering ram to break into the Krusty Krab. He looks like Pearl, but the only exception is that he has no hair.
The purple cellmate has some similarities to Squidward such as when his face resembled Squidward's when he uses chum to disguise his face and freak out the cashier. In fact, his voice sounded like Squidward and slightly sounded like Squilliam.
One of them looks like an obese version of Fred.
Reggie is the only one out of the group to have a real name confirmed.
An elderly citizen at Bikini Bottom named Dennis also appeared as one of Plankton's cellmates.