The director died Sunday of natural causes at his home in Venice, Fla., said Marc Cohen, a close family friend. O'Horgan had Alzheimer's disease.
O'Horgan made his name off-off-Broadway at such performance spaces as Caffe Cino, Judson Memorial Church and particularly La MaMa in the East Village. But it wasn't until he restaged "Hair" (taking over for another director) when the show moved from off-Broadway's Public Theater to Broadway's Biltmore Theater in April 1968 for a lengthy run -- that he was noticed by mainstream audiences.
"Tom was thoroughly theatrical," said Galt MacDermot, who wrote the music for "Hair." "He saw things in terms of theater. He gave 'Hair' a look, and he gave it movement."
Billed as the "American Tribal Love-Rock Musical," "Hair" celebrated the Age of Aquarius, a generation of antiestablishment young people brought together by sex, drugs, music and their opposition to the Vietnam War.
"Tom made the story much more about the war and Claude [one of its main characters] going to it," MacDermot added. "The writing was all there, but he reordered it and made the show more of an ensemble piece."
O'Horgan also scored with his flamboyant, often campy stage version of "Jesus Christ Superstar" (1971), featuring a score by Andrew Lloyd Webber and Tim Rice. The musical, which starred Jeff Fenholt as Jesus and Ben Vereen as Judas, ran for more than 700 performances.
Among O'Horgan's other notable Broadway productions was "Lenny," a play by Julian Berry about the fabled comedian Lenny Bruce, who was portrayed by Cliff Gorman. He also directed the musical revue "Inner City."
Among his more notable off-Broadway productions were Rochelle Owens' "Futz!" and Paul Foster's "Tom Paine," both in 1968.
O'Horgan's later Broadway-directed efforts were not successful.
Several, such as the musical "Dude" (1972) and the play "The Leaf People" (1975), folded quickly. His last Broadway project, the musical "Senator Joe" about Joseph McCarthy (for which O'Horgan wrote the music and directed), closed during previews.
O'Horgan was born in Chicago and studied music at DePaul University, earning bachelor's and master's degrees.
Throughout his life he collected musical instruments and filled his New York City loft with the pieces he accumulated until moving to Florida in 2007.