James, 56, 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.
"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, who used the "Super Freak" bass line in his hit "You Can't Touch This."
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.
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 not married and names of survivors were not immediately available, Murthy said. Funeral arrangements were being planned.