•His family did not share a cause of death, but O'Neal was diagnosed with chronic leukaemia in 2001 and prostate cancer in 2012.
•"My dad passed away peacefully today, with his loving team by his side supporting him," Patrick O'Neal wrote on Instagram on Friday.
American actor Ryan O'Neal, best known for his Oscar-nominated role in 1970 romance Love Story, has died at the age of 82, his son said.
His family did not share a cause of death, but O'Neal was diagnosed with chronic leukaemia in 2001 and prostate cancer in 2012.
He also starred in 1970s hits What's Up, Doc?, Paper Moon and A Bridge Too Far.
His son said his father was "a Hollywood legend. Full stop."
"My dad passed away peacefully today, with his loving team by his side supporting him," Patrick O'Neal wrote on Instagram on Friday.
He added that his father had always been his hero.
O'Neal's rugged good looks catapulted him from television soap to movie stardom in tearjerker Love Story. He starred as an upper-crust Harvard undergraduate who falls in love with a working class student, played by Ali MacGraw.
The movie is considered by the American Film Institute to be among the top 10 most romantic of all time.
He went on to star in 1972 screwball comedy What's Up, Doc?, alongside Barbra Streisand. He acted with her again in The Main Event in 1979.
"So sad to hear the news of Ryan O'Neal's passing," Streisand posted on X, formerly Twitter.
"He was funny and charming, and he will be remembered," she added.
He played a Depression-era conman in road comedy-drama Paper Moon (1973), alongside his nine-year-old daughter, Tatum O'Neal, who won an Oscar for her show-stealing supporting role.
O'Neal also appeared with an all-star cast in 1977 war epic A Bridge Too Far and in Barry Lyndon (1975), Stanley Kubrick's highly anticipated follow-up to A Clockwork Orange.
But his star faded at the end of the 1970s and only his turbulent personal life kept him in the headlines.
He was born in Los Angeles in 1941 to a mother who was a stage actress and a father who was a novelist and screenwriter.
O'Neal took up boxing in school and developed an impressive physique before landing small television roles.
He was cast in Peyton Place, known as America's first prime-time soap opera. That role made him a household name, and like his co-star Mia Farrow, he was able to make the leap to the big screen.
He was married twice: first to American actress Joanna Moore, with whom he had two children, including Tatum, and then to Emmy-winning actress Leigh Taylor-Young, with whom he had one son, Patrick.
But O'Neal was also known for his long-term, tumultuous romance with actress Farrah Fawcett. That relationship lasted from 1979 to 1997, and then from 2001 until Fawcett's death in 2009.
In an interview with Piers Morgan in 2011, O'Neal said that re-watching his film Love Story "upsets me, actually".
"I lost Farrah to cancer, and I just wonder [why] that played out that way for me," O'Neal said.
In the tribute to his father, Patrick O'Neal said that he was "skilled at his craft, worked so hard, and just loved acting plain and simple".
"As a human being, my father was as generous as they come," he added. "And the funniest person in any room. And the most handsome clearly, but also the most charming. Lethal combo."
Patrick also paid tribute to Fawcett, his father's long-time love.
"Now they meet again. Farrah and Ryan. He has missed her terribly. What an embrace that must be. Together again."