Where is the surprise in that? After all, the 71-year-old history of the Oscars to date is rife with British theatre names, including John Gielgud and Peggy Ashcroft - both of whom were in their seventies when they won supporting actor trophies (for Arthur and A Passage to India, respectively) - and Laurence Olivier, whose 1948 Best Actor prize for Hamlet in no way severed him from the stage in Britain, where, 15 years later, he would found the National Theatre.
But perhaps no actor of his generation - McKellen is now 59 - has appeared so purely theatrical as the man who has often been compared to Olivier in his tenacious commitment to the stage (the National, in particular) and to the tenets of the ensemble that Olivier pioneered before him. Indeed, there is always the feeling that McKellen's high-style classical bravura itself represents a throwback to an Olivier-like grandeur, very much at odds with the kind of performance that prevails on screen today.
Put another way, you wouldn't want to see McKellen's fellow nominees Nick Nolte and Tom Hanks play Romeo, Macbeth or Vanya, though on the evidence of American History X, the nominee Edward Norton might make a compelling Coriolanus.
Equally, McKellen's efforts on the screen have always suggested the strain in his efforts to achieve the stylistic self-effacement that enables most contemporary film stars less to "act" than simply to "be". If anything seemed to work against a screen career for McKellen, it was the feeling that his talent and his style were too big - their particular machinery, however brilliant, always a shade too evident - for the big screen.
Still, this is an actor who doesn't do the expected. After all, a different British actor might have taken the occasion on 9 February, the day of the Oscar nominations, to be in Hollywood already, prepared to begin the six-week onslaught of promotional activity and pressing the flesh that - more than ever - gives the run-up to the Academy Awards the air of a political campaign. Not McKellen. That same day, he was at the West Yorkshire Playhouse in Leeds - a city that doesn't feature in the Rolodexes of most American entertainment reporters - preparing to open as Prospero in The Tempest. McKellen was in Leeds because he had turned his back on the West End, as no longer providing real audiences from the community at large. It was characteristic that McKellen should be where one would least expect to find him; all the more reason why it may be he - and not either of his main rivals Nolte and Roberto Benigni (the dark horse candidate) - who steps up to the Oscar podium tomorrow evening.
"Ian has always had an enormous appetite for life and for new experience and a great curiosity about new experiences," says his friend of some 20 years, Martin Sherman, the London-based American dramatist whose play Bent was to become a rallying cry for McKellen when the actor revived it in 1990, this time as an "out" gay man. For no discussion of McKellen can even begin without ascribing the very real renewed energy of his career to a decision just over a decade ago - spurred on by Clause 28, a legacy of the same Thatcher government that in 1991 gave the actor his knighthood - to make public his homosexuality (to Peregrine Worsthorne, of all people, on Radio 3). There's a particular aptness, then, to the acclaim that he has received for his screen performance in Gods and Monsters, as James Whale, the "out" gay film-maker of the Frankenstein movies.
"The biggest advantage is that I'm more self-confident as a person," McKellen said recently. "So everything in my life is better, including my work." Knowing whereof he speaks as a gay man, he fully inhabits the realm of desire and yearning that his haunted screen character does. In Gods and Monsters, you feel, McKellen is working not just from the head but, crucially, from the heart.
It's possible, indeed, to talk of McKellen's career in terms of before and after his 1988 declaration. He has repeatedly mentioned "despising the Ian McKellen of the 49 years" prior to coming out.
He spent an essentially solitary childhood - alone, he has said, if not necessarily lonely - around Wigan and Burnley in the north of England. The isolation he may have felt was clearly compounded by the death of his mother when he was just 12. At 24, McKellen lost his father in a car crash and was prepared to find in the theatre a replacement for the family he had lost.
McKellen developed an interest in the theatre while a scholarship student at St Catherine's College, Cambridge, where he read English and was a university contemporary of David Frost, Derek Jacobi, and Trevor Nunn, the last of whom would go on to direct several of the actor's greatest performances to date.
"I entered the theatre to meet gay men," McKellen has more than once explained. But behind the apparent breeziness of the remark lay his awareness that the stage, in some fundamental way, was home. His first West End play was at the Duke of York's in 1964, in A Scent of Flowers, for which he won the Clarence Derwent Award. But it wasn't until he joined the Royal Shakespeare Company in 1974 - and the National, a decade later - that he began to stake his claim to be his generation's finest classical actor.
To some, that accolade has always been tempered by an awareness of McKellen's penchant for "acting" a part. As recently as 18 months ago, when he opened Nunn's National Theatre regime playing Stockmann in An Enemy of the People, there were those observers who were put off by the fidgets and tics of the performance, even as others applauded the way in which Ibsen's dogmatic crusader was startlingly transformed into a zealous hysteric and borderline fascist.
As Richard III in the same theatre, his performance that spawned the 1995 film directed by Richard Loncraine that, it is said, left McKellen a scant two votes away from an earlier Oscar nomination. His Mosley-esque blackshirt of a Richard left the occasional observer dismayed by the vocal and physical embellishments even as the majority were swept up by McKellen's cold and hissing way into a role that - in the film - finds the actor beginning the opening soliloquy in the loo.
It's tempting to think of McKellen as a Meryl Streep of the stage, in that his seemingly limitless technique is the source of his greatness, and of the odd dissenting opinion. Indeed, one of the pleasures of his performance as Garry Essendine in Leeds in December in the West Yorkshire Playhouse revival of Noel Coward's Present Laughter was the clear fun the actor was having in sending up (among others) himself. Although McKellen was, by his own definition at least, a decade too old for the role, his Garry was a deliciously preening, self-absorbed ham, as played by an actor who has certainly supped at that table but also has the integrity to cut, sharply and mercilessly, to the quick.
It's that fiercely intelligent and incisive streak that won McKellen Broadway's Tony Award for Best Actor in 1981, playing a Salieri, in Peter Shaffer's Amadeus, whose tragedy lay in self-knowledge. Here was a self- described "mediocrity" whose genius lay in recognising the latter quality in others (pre-eminently Mozart) even as the court composer knew he possessed none of it himself. As Iago in Trevor Nunn's studio Othello in 1989, the actor redefined for ever a glassy-eyed Machiavelli from whom all compassion had been scarily cut away. His penultimate line, "what you know, you know," registered a guile and cunning made even more terrifying by being unknowable.
Indeed, if there's anything particularly sweet about McKellen's inclusion in the Oscars this year, it must be the possibility that he and Judi Dench could win trophies the same night, in so far as the two are long-time colleagues and friends and continue to be regarded as the best of all modern-day Macbeths in another Nunn RSC production from 1975.
And, as with Dench, it wasn't that long ago that McKellen and movies seemed an unhappy match. While Anthony Hopkins - 18 months McKellen's senior - was notching up award after award (and swearing off the theatre for ever in order to do so), McKellen was tackling Chekhov (Uncle Vanya), Ayckbourn (Henceforward...) and De Filippo (Napoli Milionaria), with film roles generally relegated to vivid extended cameos (his putative star vehicle as DH Lawrence in the little-seen Priest of Love in 1981 notwithstanding): opposite Streep in Plenty, and Stockard Channing in Six Degrees of Separation.
But, rather than sit idle, the newly politicised McKellen could use the stage as a forum for advocacy in his autobiographical solo show, A Knight Out, which became the itinerant calling-card of the post-"out" McKellen just as an earlier one-man show, Acting Shakespeare (for which he received a 1984 Tony nomination in New York) had been of the pre-"out" one. Returning to Sherman's Holocaust drama Bent at the National in 1990, 11 years after a closeted McKellen had premiered the same show playing the same gay character at the Royal Court, McKellen took a long and deserved solo bow, as if to tell the audience he was back, unbeaten and unafraid.
And that, perhaps, is the greatest paradox of all: that an actor who long kept his sexuality under wraps for fear that it might blight his career finds himself, two months from his 60th birthday, better-known and more feted than ever, while still being virtually the only internationally renowned actor who is openly gay. Indeed, McKellen's date for the Oscars will be the British theatre writer-director Sean Mathias (Les Parents Terribles, A Little Night Music), who staged the recent Bent revival and, before that, was McKellen's long-time lover. Mathias was also by McKellen's side on Broadway when the actor won his Tony 18 years ago. Receiving that award, McKellen thanked the New York audience (who "lift you so high", he said, "that sometimes you feel you want to fly for them") and his colleagues, but kept his off-stage life silent.
It's a transformed Ian McKellen, however, who is in Los Angeles this weekend. Whatever else happens during the 1999 Oscars, this much is certain: if McKellen wins, his acceptance speech alone should make it a night to remember.
Vital statistics: Born 25 May 1939. Knighted in 1979.
Education: Wigan Grammar School; Bolton School; St Catherine's College, Cambridge
Career: Professional debut in 1961 at the Belgrade Theatre, Coventry. First London appearance in 1964 in A Scent of Flowers. First appeared at the Royal Shakespeare Company in 1974 and at London's National Theatre in 1984
Films: Starring film debut in 1981 as D H Lawrence in Priest of Love, followed by Scandal, Plenty, Six Degrees of Separation, Gods and Monsters (pictured) and Apt Pupil.
Awards: Broadway's 1981 Tony Award as Salieri in Amadeus. A Golden Globe for Rasputin. Five-time Olivier Award-winner for Pillars of the Community (1977), The Alchemist (1978), Bent (1979), Wild Honey (1984), and Richard III (1991).
He says: "I now understand what the Oscars are about - they're about selling movies."
And would he like to win one? "Yes, very much."