J.J. Cohen (born Jeffrey Jay Cohen on June 22, 1965) is an American actor who has appeared on stage, in film and on television. Having gotten his start in the theatre doing musicals, Cohen's first feature film was in the 1984 film Paradise Motel and it was only a year later, in 1985, when he would get a big break in the hit film, Back to the Future as Skinhead, a member of Biff Tannen's gang. Cohen had tested for the role of Biff Tannen, and in commentary to the DVD, Robert Zemeckis and Bob Gale have stated that he had been their first choice to play Biff. Cohen was taller than Michael J. Fox, and the film creators have stated that Cohen would have been Biff had Fox been in the cast from the outset. However, after Eric Stoltz was cast as Marty McFly, it was decided that a taller actor would be needed for the film's villain.

Cohen appeared in all three parts of the Back to the Future trilogy. As with several other actors in the trilogy, Cohen played more than one role. Unlike the other actors, however, he portrayed two unrelated characters. After being seen as 1955 high-school punk Skinhead in the first film, and as a member of Biff's entourage in 1955 and 1955A in the second movie, Cohen appeared at the close of the third film as one of "Needles Gang". He is standing in the back of the pickup truck, and wearing a gold and black school jacket. Unlike Skinhead, Needles's friend wears his hair long, but his smirk is unmistakable.

But Back to the Future was just the beginning of his film credits, Cohen's other film roles include the 1985 film Secret Admirer. He starred in the 1986 drama film Fire with Fire and in the 1987 film The Principal as White Zac. He also appeared in 976-EVIL. Cohen's most recent film was in the 2000 film Almost Famous.

Cohen has appeared in many television shows, including V: The Series, Baywatch, Amazing Stories, Pacific Blue, 3rd Rock from the Sun, Providence and was a series regular on the sexy nighttime soap opera, Valley of the Dolls, playing record mogul Seth Stein.