The star of the 1962 classic Lawrence of Arabia passed away on Saturday at the age of 81. He was in hospital at the time, being treated for a long illness.
British Prime Minister David Cameron led the tributes to the acclaimed Irish actor. He said that Peter's performance "in my favourite film, Lawrence of Arabia, was stunning".
Stephen Fry also paid his respects. "Oh what terrible news," he tweeted. "Farewell Peter O'Toole. I had the honour of directing him in a scene. Monster, scholar, lover of life, genius…"
Actor David Walliams recalled his memories of the actor. "Matt (Lucas) & I had drinks with Peter O'Toole a few years ago," he said. "He was hugely entertaining. The greatest company. A legend on screen and off."
Film critic Barry Norman described him as a "true movie star" who had "tremendous charisma".
Journalist Piers Morgan tweeted, "RIP Peter O'Toole. Spent one of the funniest days of my life with him at Lord's a few years ago. A brilliant actor & crazy, hilarious man."
One of the most touching tributes came from Irish President Michael D Higgins. "Ireland, and the world, has lost one of the giants of film and theatre," he said.
"I was privileged to know him as a friend since 1969. I spent part of 1979 in Clifden where we met almost daily and all of us who knew him in the West will miss him warm humour and generous friendship."
Peter began his acting career on the British stage, and his Hamlet in 1955 at the Bristol Old Vic was critically acclaimed.
He reached international fame when he was cast as British adventurer TE Lawrence, the World War One soldier who led an Arab rebellion against the Turks.
In July 2012, after a remarkable career spanning 50 years, he announced his retirement.