Mr Cleaver died at Pomona Valley Hospital Medical Centre, a spokeswoman Leslie Porras said. She declined to provide any cause of death or any details about his hospitalisation, citing the family's request.
At times a convict, political candidate and author, Mr Cleaver was one of the original Black Panthers, formed in 1966 in Oakland by Huey P Newton and Bobby Seale. More recently, though, he denounced his past stance and joined the Republican Party.
His book, a series of powerful essays decrying prejudice and racism published in 1968, became a focus of the Black Power movement.
However, just last month, he appeared at an Earth Day conference in Portland, Oregon. "I've gone beyond civil rights and human rights to creation rights," he said. He was working as a diversity consultant.
In April 1968, Mr Cleaver, the fledgling Black Panther Party's information minister, was involved in a shoot-out with police in Oakland, California. The Panthers' treasurer, Bobby Hutton, 17, was killed in the gun battle, and Mr Cleaver and two police officers were wounded.
Mr Cleaver was arrested after the shoot-out but jumped bail of $50,000 and fled the United States.
Prior to his return to the US in 1975, he told reporters he believed he would be treated fairly in court.
"A new situation now exists in the United States. The war in Vietnam is over. The status and condition of black people has undergone a fundamental change for the better," he said.
He continued: "The American people have been shocked into objectivity and vigilance by the exposure of the massive, systematic and conspiratorial subversion of their democratic rights."Reuse content