Gruen was born in New York City. He credited Ike Turner with starting his career. He first saw Ike & Tina Turner open for Sam & Dave at New York's Felt Forum in 1969. He followed the Turners around to other gigs and took photos of them at the Honka Monka nightclub in Queens in 1970. Gruen showed Turner the photos and was invited to work with them. "Ike introduced me to the publicist for their record company who took me to parties and introduced me to more people in the music business," he said. Gruen developed a friendship with the Turners who invited him to photograph them in California. Gruen shot the cover of their 1971 album "'Nuff Said". In 2012, Gruen released , a documentary he filmed of the Turners at their home in California and on tour across the country.