Rodney King, who came to symbolise racial tensions in the United States after his 1991 beating at the hands of police led to deadly riots in Los Angeles a year later, has been found dead in a swimming pool on in Rialto, California, police said.
He was 47.
"Preliminary indications are that this is a drowning with no signs of foul play," Rialto police said in a statement.
King was discovered by his fiance, said Rialto police Captain Randy De Anda. The San Bernadino County Coroner's office will conduct an autopsy, authorities said.
King's death was reported to police Sunday morning in Rialto, about 80km east of Los Angeles. Police pulled his body from the swimming pool but were unable to resuscitate him, De Anda said.
King became known around the world after he and some friends were stopped by Los Angeles police on March 3, 1991, following a high-speed chase. King was beaten by baton-wielding officers while a bystander videotaped them. The video prompted a national debate on police brutality and race relations.
When the officers were cleared of brutality charges a year later, riots broke out in Los Angeles, resulting in 53 deaths and an estimated US$1 billion (NZ$1.27b) in damage.
During the riots, King made a famous televised appeal for calm, saying: "Can we all get along?"
Two of the officers were later convicted on federal charges of violating King's civil rights and were sentenced to prison.
A jury ordered the city of Los Angeles to pay King, who was unemployed at the time of the beating, US$3.8 million in damages.
Activist Reverend Al Sharpton called King a powerful civil rights symbol who ''made America focus on the presence of profiling and police misconduct.''
''Through all that he had gone through with his beating and his personal demons, he was never one to not call for reconciliation and for people to overcome and forgive,'' Sharpton said in a statement.
King had a history of substance abuse and previously appeared on the US cable TV programme Celebrity Rehab.
This year, two decades after the riots, King wrote a book entitled The Riot Within: My Journey from Rebellion to Redemption.
King, who has three children, was engaged to marry Cynthia Kelley, a juror in the civil suit he brought against the city of Los Angeles, according to the biography that accompanied his book.
The Los Angeles Times published a quote that King gave the newspaper earlier this year: "I would change a few things, but not that much. Yes, I would go through that night, yes I would. I said once that I wouldn't, but that's not true. It changed things. It made the world a better place."