He is neon green with a light teal fin running down his back. He also has a small light brown fedora with a purple stripe on his head.
Role in series
He steals SpongeBob's ice cream cone in line for the stand by sliding through his holes. When SpongeBob is not assertive enough, Plankton gets inside his mouth and yells at the electric Eel to hand over the ice cream or else "every waking moment of [his] life will be filled with pain and misery," making the eel cry and run away, throwing the ice cream at SpongeBob.