Jason William Mizell (21 January 1965 in Brooklyn, New York – 30 October 2002 in Jamaica, Queens, New York), known as Jam-Master Jay (or Jam Master Jay), was a founder and the DJ of Run-D.M.C., a highly influential hip-hop group, based in the Queens borough of New York City. Mizell and the other two members of Run-DMC, the MCs Darryl "DMC" McDaniels, and Joseph "Reverend Run" Simmons, were natives of the middle-class black neighborhood of Hollis, Queens.

The Run-D.M.C. songs "Jam-Master Jay", "Peter Piper", and "Daryl and Joe" herald Mizell's skills.

Mizell played bass and drums in several garage bands prior to joining Run-D.M.C.; on all of their albums from "Raising Hell" on, he played keyboards, bass, and live drums in addition to his turntable work.

Run-DMC's signature look of black sweatsuits and leather, with black-striped Adidas sneakers, was modeled after Mizell's personal clothing style.

In 1989, Mizell established the label Jam Master Jay Records, which scored a strong success in 1993 with the band Onyx. He also connected Chuck D with Def Jam co-founder Rick Rubin. (Def Jam's other founder, Russell Simmons, is the brother of DJ Run.)

In the 1990s, Mizell suffered the effects of a bad car accident and a gunshot, mirroring similarly hard times for DJ Run (rape charge) and DMC (alcohol abuse).

Mizell remained in his childhood neighborhood his entire life. He founded the Scratch DJ Academy in Manhattan for children interested in DJing.

On October 30, 2002, at 7:30 pm Mizell was shot and killed in a Merrick Boulevard recording studio in Jamaica, Queens. The other person in the room, 25-year-old Urieco Rincon, was shot in the ankle and survived.

In 2003, Kenneth "Supreme" McGriff, a convicted drug dealer and longtime friend of Murder Inc. heads Irv and Chris Gotti, was investigated for targeting Mizell because the DJ defied an industry blacklist of rapper 50 Cent that was imposed because of "Ghetto Qu'ran", a song 50 Cent wrote about McGriff's drug history.

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