US director Rob Reiner and his wife, Michele Singer Reiner, have been found dead at their Los Angeles home.
Police detectives are investigating the circumstances as an apparent homicide, city officials said.
US broadcaster CNN reported that a spokesperson for the family had confirmed Mr Reiner and his wife had died.
Los Angeles police did not confirm the identity of the deceased but did say detectives were investigating a death.
Investigators believe they suffered stab wounds and a family member is being questioned, an official said.
The official could not publicly discuss details of the investigation and spoke to the Associated Press on condition of anonymity.
The Los Angeles Fire Department says it responded to a medical aid request shortly after 3.30pm on Sunday and found a 78-year-old man and 68-year-old woman dead inside.
Watch: Investigation under way following discovery of two bodies at LA home of director Rob Reiner
Los Angeles Mayor Mayor Karen Bass and California Governor Gavin Newsom each released statements confirming that Mr Reiner, 78, and his wife, Michele, 68, had died.
"This is a devastating loss for our city and our country. Rob Reiner's contributions reverberate throughout American culture and society, and he has improved countless lives through his creative work and advocacy fighting for social and economic justice," the mayor wrote.
Los Angeles Police Department Deputy Chief Alan Hamilton yesterday evening evening told reporters that LAPD patrol officers who called to the home late yesterday afternoon discovered two bodies inside the residence.
Detectives of the LAPD's robbery-homicide unit were waiting for a search warrant before entering the home to conduct a thorough search and investigation of the premises, Chief Hamilton said.
The LAPD issued a statement on social media earlier calling the case an investigation of an "apparent homicide," although Chief Hamilton said police had not identified a suspect as of last night.
A cause of death will be made public by the Los Angeles County Medical Examiner's Office, he said.
Mr Reiner, who turned 78 in March, has long been one of the most prolific directors in Hollywood and his work includes some of the most memorable movies of the 1980s and '90s, including This is Spinal Tap, A Few Good Men, When Harry Met Sally and The Princess Bride.
As an actor, he was best remembered for his role on the TV comedy All in the Family as Mike 'Meathead' Stivic, the son-in-law and liberal foil of the lead character Archie Bunker, played by Carroll O'Connor.
His wife was at one time a photographer who took the photo of Donald Trump that appears on the cover of his book Trump: The Art of the Deal.
Aside from his Hollywood career, Mr Reiner, a native of New York City and son of the late comedy writer and actor Carl Reiner, was well known for his political activism.
He featured in advertisements taking aim at George W Bush in the 2004 presidential election and supported then-Democratic candidate John Kerry.
He also showed support for Democratic presidential hopefuls Al Gore and Hillary Clinton.
Former president Barack Obama posted on X that "beneath all of the stories he produced was a deep belief in the goodness of people—and a lifelong commitment to putting that belief into action".
California Governor Gavin Newsom said he and his wife, Jennifer Siebel Newsom, are "heartbroken by the tragic loss of Rob Reiner and Michele Singer Reiner."
"Rob was the big-hearted genius behind so many of the classic stories we love, with projects as wide-ranging as The Princess Bride to A Few Good Men. His boundless empathy made his stories timeless, teaching generations how to see goodness and righteousness in others – and encouraging us to dream bigger," Mr Newsom said in a statement.
"That empathy extended well beyond his films. Rob was a passionate advocate for children and for civil rights - from taking on Big Tobacco to fighting for marriage equality to serving as a powerful voice in early education. He made California a better place through his good works."
"Rob will be remembered for his remarkable filmography and for his extraordinary contribution to humanity," Mr Newsom said.
Mr Reiner was first married to Penny Marshall, who played Laverne in Laverne & Shirley and was also a producer and director.
He later married photographer and producer Michele Singer, with whom he has three children, Romy, Nick and Jake Reiner.
Source: AFP/Reuters/Associated Press
