When he was in the military, Caroll wrote and illustrated Harvey, a comic strip about military life. He also animated a series of black and white cartoons called Crazy Crayon. These were done under the pseudonym "Ed Spinney."
Spinney created a puppet of a cat named Picklepuss, long before he joined the inaugural cast of Sesame Street. This cat and his other friends joined Spinney in entertaining audiences of the 1960s.
As Oscar the Grouch he has written How to Be a Grouch, a Whitman Tell-A-Tale picture book.