The West Wing and Cheers actor Roger Rees had died at the age of 71, his representative confirmed.
Rick Miramontez said Rees died on Friday night at his home in New York after a brief illness. The actor had abruptly left Durrenmatt's The Visit on Broadway in late May to undergo a medical procedure.
Wales-born Rees was an accomplished stage star who won Tony and Olivier Awards in 1982 for his role as the title character in the Royal Shakespeare Company's The Life And Adventures Of Nicholas Nickleby.
He was familiar to television audiences as Robin Colcord, a millionaire love interest for Rebecca Howe (Kirstie Alley) in 1980s comedy Cheers and more recently as British ambassador Lord John Marbury in cult US political drama The West Wing from 2000 to 2005.
Among his other credits was an appearance as the Sheriff of Rottingham in Mel Brooks' slapstick comedy Robin Hood: Men in Tights in 1993.
Fans paid tribute on Twitter.
Cary Elwes, who starred opposite Rees in Robin Hood: Men In Tights, tweeted: "So sad about the passing of #RogerRees. A beautiful human being and an incredible talent. My condolences to his family #rottingham #rhmit #robinhoodmenintights #melbrooks".
Actor and director Samuel West said he "woke to the sad news of Roger Rees's death" before posting pictures of the actor in high-profile stage roles.
Renowned choreographer Matthew Bourne wrote: "RIP #RogerRees - a lovely, generous & kind man & an heroic & passionate actor. We all fell in love with him in #NicholasNickleby so sad."
The musician Rick Wakeman added: "Very sad to learn of the passing of Roger Rees. I saw him last year at a Water Rats Lodge. A truly lovely man and very talented too."
Rees, originally an artist, turned to acting in the 1960s. Reports in the US, where he had lived for more than 25 years, said he had died after a short illness. He is survived by his husband, the playwright Rick Elise.
X-Men and Star Trek actor Sir Patrick Stewart said: "Brilliant actor, dear friend and colleague, witty, kind, private man, Roger Rees died this morning. A space is left that cannot be filled."
Shadow culture, media and sport secretary Chris Bryant said: "I remember Roger Rees in RSC Nicholas Nickleby as if it was yesterday. Sad to hear he's no longer with us."