Williamson was perhaps best known for his character Snappy Sammy Smoot, who appeared in Bijou and other comics.
He was intensely political, and illustrated Jerry Rubin’s Do It! and We Are Everywhere and Abbie Hoffman’s Steal this Book. He published Conspiracy Capers as a fundraiser for the legal fees of the Chicago Seven.
Williamson also worked for men’s magazines, including Gallery, Hustler, and Playboy.