Authorities are investigating an "apparent homicide" at Reiner's home in Los Angeles after police, firefighters and paramedics were called to the property on Sunday, it has been reported.
Reiner, 78, was a prolific Hollywood director and created some of the most well-known movies of the 1980s and 1990s, including legal thriller A Few Good Men in 1992 and romantic comedy When Harry Met Sally in 1989.
US actor James Woods said he and Reiner had been friends since they made 1996 thriller Ghosts Of Mississippi together.
In an online post, he said: "The studio didn't think I was old enough to do the part, but Rob fought for me.
"Political differences never stood in the way of our love and respect for each other. I am devastated by this terrible event."
Frozen actor Josh Gad described Reiner as "one of the greatest directors of our time" in a post on Instagram.
"He was simply a beautiful person. Rob Reiner and his wife Michelle were two of the most kind and caring souls you could ever imagine," he said.
"He cared so much for those who had no voices. This loss is devastating. I cannot express how much this hurts. Love you Rob and Michelle. Thank you for all you gave us."
John Cusack, who starred in Reiner's film The Sure Thing, wrote on X: "Shocked by the death of Rob Reiner - a great man."
The Lord Of The Rings star Elijah Wood, who appeared in Reiner's 1994 family film North, posted: "Horrified to hear of the passing of Rob Reiner and his wonderful wife Michelle. So much love to their kids and family."
Prominent political figures also paid tribute, including former US president Barack Obama, who wrote on X that he and his wife Michelle were "heartbroken by the tragic passing of Rob Reiner and his beloved wife, Michele".
"Rob's achievements in film and television gave us some of our most cherished stories on screen," he said.
"But 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 state governor Gavin Newsom said: "Rob will be remembered for his remarkable filmography and for his extraordinary contribution to humanity."
Reports say authorities have not yet confirmed the identities of the people found dead.
US publication Variety said a family spokesman for Reiner confirmed "the tragic passing of Michele and Rob Reiner" to them, in a statement that added: "We are heartbroken by this sudden loss, and we ask for privacy during this unbelievably difficult time."
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