Veteran actor Brian Dennehy died Wednesday at age 81, and celebrities were quick to react to the tragic news on social media.

He died of natural causes in New Haven, Conn., according to Kate Cafaro of ICM Partners, the actor's representatives.

Dennehy was known for roles in "Rambo: First Blood," "Tommy Boy" and "To Catch A Killer" and, later in his career, was praised for his stage work in plays by William Shakespeare, Anton Chekhov, Eugene O’Neill, and Arthur Miller.

'RAMBO: FIRST BLOOD' AND 'TOMMY BOY' ACTOR BRIAN DENNEHY DEAD AT 81

"Just devastated to learn that the magnificent Brian Dennehy has died. They [sic] is no one i enjoyed working with more. And there are few friends as valued in my life. I took this photo backstage when we were in Love Letters. He loved my pup Bowie," Mia Farrow wrote.

"Another day. Another piece of devastating news. For those who never got to see Brian's towering performance in 'Death of A Salesman,' it will go down as one of the crowing performances ever delivered in a stage," Josh Gad said in a tribute.

"Was lucky enough to see Brian Dennehy twice on stage, masterful in Love Letters, and monumentally heartbreaking in Death Of A Salesman. A colossus. What a loss," Lin-Manuel Miranda said.

William Shatner offered: "Condolences to the family of Brian Dennehy. A wonderfully talented actor."

While "First Blood" co-star Sylvester Stallone wrote, "The great actor Brian Dennehy has passed away. He simply was A brilliant performer ... He also was a Vietnam vet that helped me very much building the character of RAMBO The world has lost a great artist. #FirstBlood."

James Wood called the news devastating. "I’m just devastated to hear we lost my beloved friend and colleague, #BrianDennehy. We were partners on two of my favorite films, Split Image and Best Seller. I’ve never laughed so hard as we did every day on the set or off. For a big 'tough guy,' he was a sweetheart. #RIPBrian," Wood wrote.

Dennehy won two Tony Awards, a Golden Globe and was nominated for six Emmys. He was inducted into the American Theater Hall of Fame in 2010.

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He is survived by his second wife, costume designer Jennifer Arnott, and their two children, Cormac and Sarah. He also is survived by three daughters — Elizabeth, Kathleen and Deirdre — from a previous marriage to Judith Scheff.

Fox News' Tyler McCarthy and The Associated Press contributed to this report.