Sir Alec Guinness was celebrated as "a great artist" yesterday across an entertainment world stretching from George Lucas, creator of Star Wars - which he detested - to Ronald Neame, who produced several of the films containing his most acclaimed roles.

Sir Alec's death at the age of 86 inspired overwhelming praise for a man, who through his 40 years of pre-eminent film and television work and his recent bestselling books, was more widely known and admired than any of the other titanic actors of the 20th century.

All over the globe, he was a more intimate household name than Gielgud, who died earlier this year, Olivier, Peggy Ashcroft or Ralph Richardson.

But Sir Alec - who once said that he "bared his soul" once a month to an anonymous Catholic priest and to no one else - died as privately as he lived.

His end came on Saturday evening after a long illness, apparently cancer, which was kept secret even from his close friend and old acting partner Sir John Mills. "He was so keen to keep his privacy that he hadn't even told me," Sir John said yesterday.

Sir Alec was taken to King Edward VII hospital in Midhurst, West Sussex, on Thursday after a routine request from his GP. An ambulance spokesman said: "It wasn't an emergency."

He died in the hospital's Macmillan Unit. Jenny Masding, a palliative care specialist who treated him at the end, said: "Sir Alec died very peacefully." She added: "His death is a real loss."

His passing went unannounced for more than 24 hours. Yesterday a hospital spokeswoman said: "It is the family's wish that we do not give any details of the cause of his death."

He leaves his wife of 62 years, the playwright Merula Solomon, without whom he said his life would have been intolerable, and their son Matthew.

For many years he suffered from glaucoma and cataracts. A glaucoma operation was unsuccessful, although after it was performed doctors and nurses crowded round his bed writing "May the Force be with you" on pieces of paper.

A cataract operation worked, making "the world brighter than I have known it for about 40 years", he said in an interview last year. His death is understood to have been unconnected with either of these conditions.

Sir Alec, who was born illegitimate, died with the mystery of his father's identity unresolved. "I have to admit that my search for a father has been my constant speculation for 50 years," he wrote in his autobiography.

Yesterday - speaking from his home in Furness, Co Kildare - a member of the Guinness brewery family, Patrick Guinness, said he believed that Sir Alec was the natural son of his eminent great-grandfather Walter Guinness.

Walter Guinness, later Lord Moyne, was noted for his love affairs during the first 30 years of the 20th century. He is known to have had at least one natural son, whom he financially supported.

But he made it a condition that this support was kept secret in case it jeopardised his hopes of a peerage. Later a privy councillor and friend of Winston Churchill, he was assassinated in 1944 while resident minister for Egypt.

Patrick Guinness said he had heard it "honestly said as a matter of fact" in the Guinness family for many years that Sir Alec was also Moyne's son. "It could be wrong. Sir Alec very specifically says not in his autobiography but he could not really know. All you can do is put photographs of the two men together at the same age.

"There is quite a similarity. I personally think that it is true. But I cannot prove it either way. The answer may be somewhere in our family papers".

Sir Alec, who was brought up in genteel poverty by his mother, was "casually" told in adolescence that his real name was Guinness.

The name also appeared on his brief birth certificate. But nobody could explain why it was there, he said. His mother refused to discuss the subject.

Through his 2% stake in Stars Wars, the highest grossing film in history, Sir Alec was reputed to have made a Guinness-style fortune of up to £120m.

But he told a reporter: "Divide that by 20 and you might be nearer the mark", declining to elaborate. "If I tell you more, I'll end up having to open a hundred or more begging letters a day."

He complained that Star Wars - for him the unhappiest of his 67 films - had made him "a caged animal for the special effects from the word go". But George Lucas said: "I was looking for someone who was powerful yet gentle and that came across in Alec. The world has lost a great artist."

Ronald Neame, who produced Great Expectations, in which Herbert Pocket provided Sir Alec's first film part, and Oliver Twist, in which he played Fagin, and later directed him in Tunes of Glory, regarded by many critics as the summit of all Sir Alec's work, said: "He taught me more about acting than anybody else I have ever met or am likely to meet.

"He was like a chameleon - he became the character he was playing. I made six pictures with him and they were the happiest films of my entire life."

Sir John Mills, who played with him in Great Expectations and Tunes of Glory, said: "He brought to acting the ability to be utterly ordinary, yet extraordinary.

"The country has lost a truly great actor".

A tremendous character actor

Sir John Mills, interviewed on Radio 4's Today programme yesterday.

The questioner asked if he could recall the first time he worked with Sir Alec.

JM: I can. We met at the studios, because he'd been engaged to play Herbert Pocket in Great Expectations. It was, I believe, his first film. And it was a marvellous experience, it was a joy to act with him. He was slightly nervous, but his Pocket was a creation which will remain famous. He was a tremendous character actor.

Q: Were you aware then that this young man was going to go on to great things?

JM: Well, I felt after the first three minutes - there's a scene which I shall always remember, the eating scene - I felt that this was an extraordinary actor.

Q: You played together also, very many years later, in Tunes of Glory. He played the drunken colonel.

JM: Yes.

Q: Ronald Neame earlier told us that, originally, you were down for the drunken colonel, and that you more or less switched roles.

JM: It was an understanding with Alec. We were very, very close friends, and we had a talk and he said he thought it might be a good idea if we switched. Now I think that Tunes of Glory, that colonel, was the best performance he ever gave - because it was the anti-thesis of Alec.

Notes on a life in and out of the limelight

James Dean
In 1955, while making his first Hollywood film The Swan with Grace Kelly, Guinness met the young star James Dean who showed him his new Porsche.

"I heard myself saying in a voice I could hardly recognise 'Please never get in it ... If you get in that car, you will be found dead in it by this time next week.' He laughed: 'Oh shucks! Don't be so mean.' I apologised for what I had said, explaining it was lack of sleep and food. The following Friday, James Dean was dead, killed driving the car."

Ernest Hemingway
Filming Our Man in Havana later in the 1950s, he was at a tense dinner with two of life's great opposites, Ernest Hemingway and Noel Coward.

Hemingway morosely took him aside, complaining: "I can't bear another minute of Noel's inane chatter. If he wags that silly finger at me once more, I may hit him. I wouldn't kill Noel - just dust him up a little. Am I pissed?" "A little," Guinness replied. "He laughed and gave me a hug". From Blessings in Disguise, Hamish Hamilton, 1985

Sir John Gielgud
Acting in Sir John Gielgud's King Lear at the Old Vic early in the second world war: "John's grasp of public events was always rather tenuous. His heart, however, was in the right place. 'I feel so sorry', he once said, 'for those poor men sitting up there all day. They must be so cold'. He was pointing to the barrage balloons tethered over London".

Films
"The life of the theatre always suited my inclinations more than filming, but an element of success in films enabled me to provide for my wife, son and my mother in a moderately comfortable way. After a very impoverished period in my young manhood, this was important to me.

"Hunger and shoes worn down to their uppers leave a harsh mark and suspicion of the future and a determination that the experience will not be repeated".

Fame
"A few nights ago, leaving a London hotel where film stars often stay, I was astonished by the nice, chummy taxi driver, who sort of recognised my face, when he said, 'I'll leave the lights on in the back of the cab. I expect that's what you like'.

"I had a picture of myself, brightly illuminated, waving from side to side in a traffic jam, with bewildered passers-by asking each other, 'Who's the dotty old party all lit up?'. "'Put out the light', I said, 'and then put out the light'. 'Whatever you say, guv'." From A Positively Last Appearance, Hamish Hamilton, 1999

Ageing
"A Valentine card in a tiny illiterate hand. Surely I can't have sent a card to myself. Now that Dr Alzheimer looks as if he may be extending a welcome tome I can no longer be sure of these things." (1995)

Lord Olivier
"When I played Malvolio in a poor TV Twelfth Night, Larry came to the final runthrough ... Just before we went on air he said to me, 'Marvellous, old cock! I never realised Malvolio could be played as a bore'. Suchlike encouragements were part of his repertoire. Yet I was fond of him." (1996) From My Name Escapes Me - The Diary of a Retiring Actor