No more Mr Nice Guy: Ewan McGregor stars as the scheming villain in a revival of 'Othello'

There's more than a smack of the sordid bullfight about Othello. That parallel is subject, though, to several twists. It's a human being of a different race, not an animal, whom the scheming Iago reduces to a tortured, jealous wreck in the throes of a frothing fit at his feet. It's no red rag, but an emotionally charged handkerchief that the matador waves goadingly at his prey. Dragged into the ring, the innocent wives of both antagonists are killed during the course of the contest. And, also against the rules, the matador is, in the end, upstaged by the victim who is felled by his own hand.

Othello is arguably the most intense and immediate of Shakespeare's mature tragedies. Yet productions that release the play's full potential are rare. The problems that it poses for a director are part and parcel of its tremendous yet tricky brilliance. On the one hand, it would be a sentimental reading of the play that accepted Othello at his own valuation; on the other (which, for a while, was the modern orthodoxy) it is a cynical, reductive interpretation of the play that takes a steadfastly censorious view of his self-protective magniloquence. Avoiding both of these distortions and achieving a balanced view of the hero is the moral challenge to our perception that lies at the heart of the play. Few productions successfully rise to it.

Without doubt a key factor in this production selling out so quickly with tickets changing hands for up to 1,200 is the casting of Ewan McGregor.

It's sometimes argued that the play should be called "Iago", for it is Othello's right-hand man who drives the hero towards his doom. Iago is a warped, surrogate dramatist and his genre is revenge pornography (his account of Cassio's alleged horny dream about Desdemona brilliantly presses every button of perverted sexual arousal). Initially incited to vengeance when he is passed over for promotion in favour of a Sandhurst type, this chippy army man is revealed in soliloquy to be a psychopath who has to invent absurd reasons for his nihilistic hatred of the Moor.

But though Iago is a playwright who takes the exploitation of living creatures to a chilling extreme, it's sometimes forgotten just how improvisatory and hand-to-mouth are his methods. And in emphasising his diabolical ingenuity and recklessness, productions often overlook the fact that, for his plot to work at all, the character (and the actor playing him) must plausibly show why he has achieved his ironic reputation for honesty.

Michael Grandage, whose Donmar revival of the tragedy begins previewing tonight, is alert to the problems which are possibilities in disguise. Well aware of the performance history of Othello (in his earlier career as an actor, he played the idiotic Roderigo in the celebrated RSC production starring Willard White and Ian McKellen), he talks of the cultural shifts that have seen alternations in which of the two main male parts was regarded as the better role.

In the days when it was considered acceptable for white actors to play the Moor, leading thespians such as Edmund Kean played both roles during their career, as did Laurence Olivier, who portrayed Iago to Ralph Richardson's Othello at the Old Vic in 1938 and then blacked up as an ostentatiously African Moor to Frank Finlay's Iago in the 1964 National Theatre production.

But Grandage has been intent in rehearsal on shedding the weight of theatrical tradition. "Everything is on a knife-edge in this play, so you've got to get across the sense that nobody knows what is going to happen next." Iago takes enormous risks in the tissue of lies he concocts. No other Shakespearean tragedy could be averted so easily by someone stalking on and administering a strong dose of the facts to the deceived hero.

Casting is crucial to the chemistry that bubbles in a production between hero and villain. In this account, Iago is played by Ewan McGregor, last seen on stage as charming, personable Sky Masterson in Grandage's production of Guys and Dolls and better known as a screen actor who embraces both the indie end of the spectrum (Young Adam) and the mainstream (Star Wars, Moulin Rouge!).

The role of Othello is taken by Chiwetel Ejiofor who, though he has lately concentrated on movies (for directors ranging from Woody Allen to Ridley Scott), boasts an impressive list of theatrical credits.

The director talks of Ejiofor's "natural goodness" as a person and of how as a performer "he has access to such extraordinarily open qualities. He's somebody who manages to keep hold of something very, very childlike, who takes people as they come, and has faith that people can be like himself".

In casting McGregor as Othello's nemesis, Grandage says that he is getting away from the "bushy-eyed, fruity, over-sophisticated villain who seems to have it all worked out in advance" to someone who can move between "a charm that is not feigned" in the public scenes where he is "honest" Iago and the dark and perverted confidences delivered in the soliloquies.

Grandage is alert to the ways in which Iago can be construed as the malign step-brother of Hamlet (a perception that Simon Russell Beale drew on when he played the part for Sam Mendes). Both characters are essentially on suicide missions; there is a mystery at the heart of both their stories (the cause of Iago's malignity; the reason for Hamlet's fatalism after the sea voyage). And silence is the end of the road for both these loquacious soliloquisers who, in Iago's case, break the rule that characters tell only the truth when speaking directly to the audience.

The irony is that while Iago may wrestle with the unknowable nature of his motivation, he knows one thing for sure: that Othello has "a free and open nature". As with the jealousy of Salieri, the composer destructively fascinated by Mozart's genius, Iago's envy is an inverted, glowing tribute. Grandage's production looks poised to bring out the full balance of forces in this fierce, bloody bullfight.

'Othello', Donmar Warehouse, London WC2 (0870 060 6624),to 23 February