Silas Plankton is Sheldon J. Plankton's parental uncle who appears in the comic A Plankton Family Tree.
He is deep green in color and roundish, has two eyes, two antennae, buck teeth, and a faint tail.
Role in the comic
He is only in the comic as a picture and representation of Plankton's family tree. Plankton also mentions that Silas thought his nephew was marrying a piece of farm equipment.