Harold Diamond (1926-1982), was an American art dealer. Diamond worked as a teacher in New York City's public school system, later becoming an art dealer specializing in 20th-century work. He worked as a private dealer, negotiating for the discreet sale of works of art from their usually European owners to buyers who were typically American, and was known for his refusal to reveal the names of either sellers or buyers.Together with his wife Hester Diamond, they assembled "one of the great postwar collections of modern art in New York".He was married to Hester Diamond, and their son Mike D is a musician, and founding member of the Beastie Boys.