Adam Horovitz, a.k.a. King Ad-Rock, (born October 31, 1966, in South Orange, New Jersey) is a member of the Beastie Boys. After leaving his band "The Young and the Useless", Adam Horovitz joined Mike D and MCA in the Beastie Boys, opening for Madonna on her famous Like a Virgin tour.

He plays the guitar, and is also an M.C. who writes and performs lyrics which have influenced the development of both hip hop and rock music. He currently resides in New York City. His father is the playwright and screenwriter Israel Horovitz and the film Author! Author! is based on the experiences of the real-life Horovitz family. He dated Molly Ringwald (1986-1988), Ione Skye (1988-1991, married 1991-1999), Kathleen Hanna (1996 to present). He has appeared in the following movies: Lost Angels, Roadside Prophets, and A Kiss Before Dying.

As well as his work with the Beastie Boys, Horovitz also has a side-project by the name of BS 2000.