Isaac Hayes, the 1970s king of soul and funk who became known to a new generation as a baritone-voiced cartoon chef, died last night. He was 65.

The Oscar-winning singer-song-writer, who came to prominence with the theme tune from the 1971 “blaxploitation” film Shaft, was found by members of his family, near a treadmill – which was still running – at his home in Memphis, Tennessee. The cause of death was not clear.

Hayes was one of the dominant black musicians of the 1970s alongside Al Green, James Brown and Stevie Wonder, and is credited with laying the groundwork for disco and rap music.

The self-taught musician was hired in 1964 by Stax Records as a back-up pianist, working as a session musician for Otis Redding among others. The release of his album Hot Buttered Soul in 1969 made him a star, although it was the theme tune for Shaft two years later, which won an Oscar, that propelled him into the super league.

Always an arresting sight, with shaven head, gold chain and sunglasses, Hayes became a musical innovator and a figurehead for the black civil rights movement throughout the 1960s. During an interview in the late 1990s he said of his career: “The rappers have gone in and created a lot of hit music based upon my influence. And they’ll tell you if you ask.” He was elected to the Rock’n’Roll Hall of Fame in 2002.

Last night Don Cornelius, the founder of the Soul Train TV series in the US, described him as “a real power-house in music”. He added: “He took black music to another level, made it more classic.”

Hayes used his rich baritone as the voice of Chef, the school cook and devoted ladies man, in the South Park cartoon series. Chocolate Salty Balls, his South Park single, reached No 1 in the British charts. He left the series in 2006 in protest at its portrayal of Scientology.

Hayes was also involved with humanitarian work. In 1995 he established the Isaac Hayes Foundation, which worked to increase literacy. He travelled frequently to Ghana, where he helped to fund a school. He was even made a Ghanaian king with the title Nene Katey Ocansey. In 2005, he married a Ghanaian woman – his fourth marriage. He had 12 children.

Steve Shular, a spokesman for the Shelby County Sheriff’s Office said that Hayes’s wife found him collapsed in a bedroom when she returned from a grocery store. He said: “The treadmill was running but he was unresponsive lying on the floor.”

Hayes, who described himself as a health fanatic, had a stroke last year.

From Stax to Chef

— Isaac Hayes was born into a sharecropper’s family in 1942, in Tennessee, near Memphis. Orphaned in infancy, he was raised by maternal grandparents

— Hayes began his recording career in the Sixties, as a session player for various acts of the Memphis-based Stax Records. He made his breakthrough in 1969 with the LP Hot Buttered Soul

— In 1971 Shaft was released. The film’s soundtrack was the first album by a solo black artist to reach No 1 in the pop and R&B chart. Hayes won the Oscar for Best Musical Score

— He began his own record label in 1975 in which he adapted to disco

— In 1997 he became the voice of Chef in South Park, the TV animation