Sheldon J. Plankton and Karen Plankton are a pair of fictional characters and the main antagonists of SpongeBob SquarePants, the Nickelodeon animated television series. They are respectively voiced by Mr. Lawrence and Jill Talley. Their first appearance was in the episode "Plankton!" that premiered on July 31, 1999. They were created and designed by the marine biologist and animator Stephen Hillenburg, the creator of the series. Hillenburg named Karen after his wife, Karen Hillenburg (née Umland