US actor Leonard Nimoy, who played Mr Spock in the cult sci-fi series Star Trek, has died at the age of 83 in Los Angeles, his family has said.
His son, Adam, said he died of end-stage chronic obstructive pulmonary disease on Friday morning.
Nimoy had a long career as both an actor and director.
However he was best known for his portrayal of the half-human, half-Vulcan character in both the TV franchise and series of films.
Last year, the actor revealed he was suffering from chronic lung disease, despite stopping smoking 30 years ago.
It was reported earlier this week he had been taken to hospital on 19 February after suffering from chest pains.
He later tweeted: "A life is like a garden. Perfect moments can be had, but not preserved, except in memory."
He signed off with "LLAP" - a reference to his character's famous catchphrase, "Live long and prosper". It was to be his final tweet.
George Takei, who played Hikaru Sulu on Star Trek and was a friend of Nimoy's, paid tribute to the actor.
"The word extraordinary is often overused but I think it's really appropriate for Leonard", Mr Takei told US broadcaster MSNBC.
"He was an extraordinarily talented man but he was also a very decent human being."
Among the torrent of tributes on Twitter was a message from Nasa with a picture of the actor standing in front of a replica Space Shuttle.
Thousands took to Twitter to pay tribute after Nimoy's death was announced, including Star Trek actors past and present.
William Shatner, who as Captain Kirk acted alongside Nimoy for years in Star Trek, said he loved the actor "like a brother".
"We will all miss his humor, his talent, and his capacity to love," Mr Shatner said on Twitter.
Wil Wheaton, who played Wesley Crusher in Star Trek: The Next Generation, said: "We stood on your shoulders, and wouldn't have had a galaxy to explore if you hadn't been there, first. Thank you, Leonard, Rest in peace."
