Before Shaft, scores for exploitation flicks were mostly incidental music, with maybe a theme song over the credits. Hayes's jazz funk sound-track for Shaft incorporated rap and gospel-style vocals, underscoring the action on screen like a Greek chorus.
The eponymous private dick, would manoeuvre his Afro hairstyle through the door of some thieves' den, take out a gun with an improbably phallic silencer, and dispatch the miscreants while the girl singers chanted Shaft's name, and Hayes, with his distinctive fur-lined voice, intoned slogans such as "Can you dig it?", and "That cat Shaft is a baad mutha."
Not exactly Cole Porter, but the style established by Hayes in Shaft - wedding the sounds of contemporary American black neighbourhoods to established Afro-American musical traditions - was much copied and became the defining element of the "blaxploitation" movie genre, to which Quentin Tarantino paid homage in his film Jackie Brown. But his musical achievements are much more than that.
Born of poor sharecroppers in Tennessee, in 1942, and raised by grandparents, Hayes absorbed a tradition of black music stretching back to the turn of the century. "Sitting on the porch, I'd sing the old Negro spirituals with my family," says Hayes.
While still in his teens, he was hired as a sideman by Stax Records in Memphis, whose releases were felt by many to be a purer, less commercial, less white version of black music than those on the more successful Tamla Motown label. As keyboard player, vocalist, and composer, Isaac Hayes was a key figure in creating the Stax sound.
He played on sessions with Booker T and the MGs, Sam and Dave, and Otis Redding, and wrote hits including "Soul Man", "You Don't Know Like I Know", and "Hold On, I'm Coming". When Stax gave Hayes the chance to release solo projects in the late Sixties, he revolutionised rhythm and blues music.
He would take white cocktail bar songs such as "Walk On By" and "By the Time I Get to Phoenix" and claim them for black music, with lengthy jazzy arrangements and almost spoken vocals. Hayes's unique style was undoubtedly a forerunner of disco and rap, and others benefited from what he had created while Hayes's own career went into a decline, embracing bankruptcy, and a spell in prison for drug offences.
His recent glorious resurrection owes less to his albums, which remain as inventive as ever, than to his incarnation as the character Chef, head of the school cafeteria in South Park, the crudely drawn and even more crudely spoken cartoon series. South Park will never be The Simpsons, but what patina of sophistication it has is lent to it by the lovable Isaac Hayes character.
In his live act, he now performs the South Park song "Love Gravy", which is about a drunken pig making "sweet lurve" to a drunken elephant, which could be interpreted as an oblique, ironic comment on performers such as Barry White, who took Hayes's symphonic soul and commercialised it.
This is probably not intentional. It may simply be Hayes's way of showing gratitude for the fact that, for whatever reason, his maverick genius is gaining some recognition. At last, a reason to give thanks for cable television.