Adam Keefe Horovitz, better known as Ad-Rock or King Ad-Rock, is an American rapper, guitarist and actor. He is best known as a member of the hip hop group the Beastie Boys. He is married to musician and feminist activist Kathleen Hanna.

Horovitz began his music career with a stint in the punk rock band the Young and the Useless, who would often perform with the Beastie Boys. In 1982, Beastie Boys guitarist John Berry quit and Horovitz replaced him. He was only 16 at the time. After Horovitz joined the band, the Beastie Boys changed their sound, evolving from a hardcore punk band to a more hip-hop oriented group. The band was signed to Def Jam, and released their debut album Licensed to Ill in 1986. The album was a huge commercial success, and spawned six hit singles. Seven further albums followed, and by 2010 the Beastie Boys had sold 22 million records in the United States alone, and 40 million worldwide. In 2012, the Beastie Boys were inducted into the Rock and Roll Hall of Fame.

In addition to his work with the Beastie Boys, Horovitz also remixes numerous tracks for other artists under the alias 41 Small Stars. He plays bass in The Tender Moments, the backing band of New York-based cabaret performer Bridget Everett.

Horovitz has also acted in several motion pictures and television shows. Some of his roles include Tim 'Chino' Doolan in Lost Angels, Sam in Roadside Prophets, Repulski in Godspeed, Fletcher in While We're Young, and Nick in Golden Exits.

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