He grew up in the Bronx, born to Polish Jewish immigrant parents who didn't believe in his calling. “I remember once picking up a copy of Life magazine and saying to them, ‘A page in this magazine would cost an advertiser $50,000, of course you can make a living in this field,’” he recalls. “But I couldn’t convince them. They wanted me to be an accountant.”
Gersten studied at the Cooper Union Art School, and Cooper School of Design, before establishing his career as a caricaturist. He drew hundreds of illustrations for publications such as The New York Times, New York Magazine, Sports Illustrated, Time, Newsweek, Harpers, Rolling Stone, Esquire, Harper's and Playboy. His work also adorned many record covers for RCA. On March 29, 1973 his work adorned the cover of Rolling Stone, with a lively depiction of Dr. Hook & the Medicine Show.
In 1986, he began work for MAD Magazine, drawing political caricatures of public figures, for MAD's brand of satire.