James died in his sleep at his residence near Universal City, said publicist Sujata Murthy. James lived alone and was found dead by his personal assistant, who notified police, she said.
Police and Murthy believe James died of natural causes. The exact cause was not immediately released.
"There'll be an autopsy and we'll find that out shortly," Murthy said.
Publicist Maureen O'Connor, speaking on behalf of James' three children, said they believed he died of heart failure.
"He passed away peacefully in his sleep," O'Connor said.
"I think he was really fantastic, he was a creator," singer Little Richard told MSNBC.
"He made a lot of people happy, he made a lot of friends and a lot of people got famous through his music," he said, referring to sampling by hip-hop artists such as MC Hammer (search), who used the "Super Freak" bass line in his hit "U Can't Touch This."
The song earned James and Hammer the Grammy for best R&B song in 1990.
"Today the world mourns a musician and performer of the funkiest kind," said Neil Portnow, president of the National Academy of Recording Arts and Sciences. "Grammy winner Rick James was a singer, songwriter and producer whose performances were always as dynamic as his personality. The 'Super Freak' of funk will be missed."
James had hit songs and albums from the 1970s into the '80s, but by the following decade his fame began to fade as he became embroiled in legal problems and health troubles.
James was convicted in 1993 of assaulting two women. The first attack occurred in 1991 when he restrained and burned a young woman with a hot pipe during a cocaine binge at his house in West Hollywood. He was free on bail when the second assault occurred in 1992 in James' hotel room.
James served more than two years in Folsom Prison (search).
In 1997, he released a new album, but a year later he suffered a stroke while performing at Denver's Mammoth Events Center, derailing a comeback tour.
In 1998 he also underwent hip replacement surgery.
James was born James A. Johnson Jr. in Buffalo, N.Y. He had long been reported to have been born in 1952, but according to his Web site and police he was born on Feb. 1, 1948.
James went to work for Motown in the 1970s and got the chance to record an album, "Come and Get It," which was released in 1978 and produced the hit "You and I." He followed with "Bustin' out of L Seven," which had a hit with the single "Bustin' Out," and another popular LP, "Fire it Up."
His hits in 1980 included the album "Garden of Love" and the singles "Fool on the Street," "Love Gun," "Come into My Life," and "Big Time." The following year came the well-received album "Street Songs" and the hits "Give It to Me Baby" and "Super Freak."
After a decade at Motown (search), James left the label as the sexually graphic themes of his music conflicted with the company's conservative approach to pop music.
"They never totally understood what I was trying to do, where I was trying to come from with my music," he said in a 1988 interview with The Associated Press. "For the whole 10 years, it was a constant battle in me trying to acquaint them with what I wanted to say and how I wanted to say it."
At the time he said he had freed himself from a cocaine addiction that threatened his life.
"There was a bad period in my life some years ago when I got into a serious cocaine habit; $10,000 to $15,000 a week," he said. "I didn't really see it. My lawyers and my accountants and friends really saw it before I did. They saw that my usage of coke was getting to be a million-dollar-a-year habit. I didn't see it until I went into rehab and I didn't understand it until I got out."
James said he got caught up in living the "bad boy" persona he had cultivated.
"There was a time where I was just trying to live the image wholeheartedly; I wasn't thinking about the person, James Johnson," he said. "I mean, Rick James was just a man-made image, the image I created. Just trying to live Rick James almost killed me."
James was not married, Murthy said. He is survived by daughter Ty, sons Rick Jr. and Tazman, and granddaughters Jasmine and Charisma.