Alec Guinness lacked many of the advantages of his theatrical peers. He could not claim Olivier's outstanding good looks and pure animal magnetism: he was bald by the time he reached 32, which emphasised his pointy, puckish ears. Unlike Gielgud he was not steeped in theatrical tradition: his childhood was disrupted and unhappy and his most vivid memory was of Nellie Wallace in music-hall at the Coliseum. He lacked Richardson's ability to be a "card", and he certainly did not have the Richardson ruthlessness, which ensured that Ralph was never upstaged: late in his life Guinness remarked, a little ruefully, "I'm not a very confident person, never have been."

But he had one great gift denied the others: anonymity. On stage or on screen Olivier was always Olivier, Gielgud always Gielgud and Richardson always Richardson. Guinness had the ability to obliterate himself completely within each character he played.

He was a master of disguise, and some of his critics claimed that he achieved this by building around himself a carapace of privacy and mystery. Such an explanation is too superficial. Guinness achieved much of his distinction by sheer graft, aided by high intelligence and a gift for acute observation.

His beginnings in the theatre before the war were uncertain. It took him two years to get a commission in the Royal Navy during the war, and his command of a rickety landing craft in the Mediterranean had its inglorious moments, as he recounted with some irony in his autobiography Blessings in Disguise.

In the cinema his great mentor was David Lean, who gave Guinness his first major role in Great Expectations and later established him as a truly international star in films such as The Bridge on the River Kwai and Lawrence of Arabia. Director and star had several well publicised rows. But the two men needed one another.

Guinness was rare among actors in being a master of self-deprecation. He once said: "Essentially I'm a small-part actor who's been lucky enough to play leading roles for most of his life." For luck read good judgment. Guinness knew what was beyond his reach. After the early days his excursions into Shakespeare were comparatively rare and on the whole not very successful. He attempted Lear only on radio when he was well on in life. He shied away from the avant-garde, getting no closer to it than Ionesco's Exit the King at the Royal Court. Alec Guinness believed in the art of the possible.

Offstage Guinness usually tried to be just a face in the well-behaved crowd and generally succeeded. No breath of scandal touched his marriage of over sixty years, and he was rarely stalked by the gossip columnists. He liked good restaurants, especially the Connaught, but there again he blended into the background. He was fond of telling the story of how he handed in his coat at a hotel cloakroom and, offering to give his name, was quite pleased to be told that it would not be necessary. The coat was later handed back with the ticket still attached and on it the inscription "Bald with glasses".

Alec Guinness was illegitimate and no father's name appeared on his birth certificate. There have been suggestions that the man in question was a middle-aged banker called Geddes. His mother, Agnes de Cuffe, a temporary barmaid, did not admit to her son for several years that Guinness was not his real name.

She was married briefly to a self-styled "Captain" David Stiven, who treated his stepson brutally. Agnes was little better, leaving behind her a trail of unpaid bills at cheap London hotels. Guinness had as little affection for her as John Osborne had for his monstrous mother Nellie Beatrice, although unlike Osborne he was too polite to vent his dislike in public. School was little better than home, as he moved through a succession of undistinguished South Coast establishments. By 18 he had found a modest job in a London advertising agency and cut off all relations with his mother.

He got a little training at the Fay Compton School of Dramatic Art, and plucked up the courage to write to John Gielgud, ten years older than Guinness and already an idol. Gielgud, who had been a judge at the Fay Compton end- of-term performance, engaged him as Osric and Third Player for the Hamlet he was preparing for the New Theatre in 1934 and stuffed a few much-needed shillings in Guinness's pocket. Guinness always claimed that it was Gielgud who launched him on his career, but an equal influence was the flamboyant Martita Hunt. She regularly told him that he had little talent, but encouraged him nonetheless and her coaching helped to get him his drama school scholarship. The two were to meet again twenty years later when Hunt played Miss Havisham in Great Expectations.

Guinness had a season with the Old Vic Company in 1936-37, playing a number of small roles and one quite large one, Sir Andrew Aguecheek in Tyrone Guthrie's production of Twelfth Night. He worked there with Michael St Denis, but Guthrie himself was to be far the greater influence.

Guthrie took him on tour with Hamlet to Elsinore to play before the royalty of Denmark and Sweden. His parting words before the first night were: "Be polite to Kings and Queens if they get in your way, Alec." Guinness, fortified by some schnapps to keep the Danish cold out, duly laid his sword on the King of Sweden's lap. Despite such indiscretions Guthrie thought his protege good enough to play the title role, which he did under Guthrie's direction in 1938. This was reasonably well received and even drew some encouraging words from Gielgud, but it did not greatly stir the public.