He was contacted by his cousin Sheldon J. Plankton, who needed his family's help to obtain Krabby Patty secret formula. He is introduced as the leader of the rest of Plankton's cousins, since he does most of the speaking. Clem re-introduced Sheldon to his family, when he seemed unfamiliar with them. But after going on and on introducing the hundreds of the family members, Plankton screams at him to stop.
"One Coarse Meal"
He appears in Plankton's flashback about his family being eaten, and then appears again inside Pearl during Plankton's nightmare.
He was the character who revealed Plankton's first name.