Yasiin Bey /jæˈsiːn ˈbeɪ/ (born Dante Terrell Smith on December 11, 1973), better known by his former stage name Mos Def /ˈmoʊs ˈdɛf/, is an American actor and hip hop recording artist from Brooklyn, New York City, New York. He is the host of Def Poetry Jam which aired on HBO between 2002 and 2007. Best known for his music, Mos Def began his hip hop career in 1994 in the short-lived rap group UTD or Urban Thermo Dynamics, after which he appeared on albums by Da Bush Babees and De La Soul. Alongside Talib Kweli, he formed the duo Black Star, which released the album Black Star in 1998. He was a major force in late-1990s underground hip hop while with Rawkus Records. As a solo artist he has released the albums Black on Both Sides in 1999, The New Danger in 2004, True Magic in 2006, and The Ecstatic in 2009.

Prior to his career in music, Mos Def entered public light as a child actor, having played roles in television movies, sitcoms and theater, some of which were under the name Dante Beze. At the age of 14, he appeared in the TV movie God Bless the Child which aired on ABC in 1988. He played the oldest child in the 1990 family sitcom, You Take the Kids, shortly before it was cancelled. In 1995, he played the character "Dante" in The Cosby Mysteries. Since the early 2000s, Mos Def is well known for his roles in films such as Something the Lord Made, Next Day Air, The Hitchhiker's Guide to the Galaxy, 16 Blocks, Be Kind Rewind, The Italian Job, and his portrayal of Brother Sam in the American drama series Dexter. Mos Def has also been vocal on several social and political causes.