Yasiin Bey ( yass-EEN BAY; born Dante Terrell Smith; December 11, 1973), formerly known as Mos Def ( MOHSS DEF), is an American rapper and actor. A prominent figure in conscious hip hop, he is recognized for his use of wordplay and commentary on social and political issues, such as police brutality, American exceptionalism, and the status of African Americans in the United States.

After embarking on his career in 1994, he joined his siblings in the short-lived rap group Urban Thermo Dynamics (UTD) and guest appeared on albums by Da Bush Babees and De La Soul. In 1996, he and fellow Brooklyn-based rapper Talib Kweli formed the duo Black Star, whose debut album Mos Def & Talib Kweli Are Black Star (1998) spawned the singles "Definition" and "Respiration" (featuring Common). His debut solo album, Black on Both Sides (1999) was met with critical acclaim, along with his fourth album The Ecstatic (2009). Bey's 2000 single, "Oh No" (with Pharoahe Monch featuring Nate Dogg) remains his sole entry on the Billboard Hot 100 as a solo act. In 2014, About.com listed him 14th on its "50 Greatest Rappers of All Time".

A former child actor in television films, sitcoms, and theater, Bey has appeared in the films Something the Lord Made, Next Day Air, The Hitchhiker's Guide to the Galaxy, 16 Blocks, Be Kind Rewind, The Italian Job, The Woodsman, Bamboozled, and Brown Sugar and in television series such as Dexter and House. He hosted Def Poetry Jam from 2002 to 2007.