The Malcontent, RSC Swan, Statford-upon-Avon

If the Elizabethan and Jacobean repertoire did not exist, you fancy that Antony Sher would have been forced to invent it. This neck of the dramatic woods provides him with the kind of outsize, stage-dominating roles – from Richard III to Vindice and Tamburlaine – that he devours for breakfast. In the current Stratford season, he is already chewing the scenery with his blackly comic portrayal of a megalomaniac emperor in Massinger's The Roman Actor. To this feat, he now adds a balefully witty bravura performance in the title role in The Malcontent, John Marston's 1603 tragicomedy, which is sparkily revived by Dominic Cooke in a production that transposes its Renaissance intrigues to a Latin American military dictatorship in the 1970s.

Like the Duke in Measure for Measure, Altofront returns to his court in disguise. But there the resemblance between them ends. He, by contrast, has lost the dukedom of Genoa to a usurper, Pietro, whose regime is propped up by a marriage-cemented alliance with Florence. But "Malevole", the persona he adopts, is no straightforward revenge-intriguer plotting for a bloody comeback. Instead, he assumes the role of a professional cynic, an observer who splenetically castigates the corruptions of the greedy, sex-mad, politically fickle court, while exploiting whatever chances come his way (like the adulterous behaviour of the new duchess) to exact psychological vengeance on his supplanter and to join forces with him against the greater evil embodied in the ambitious Machiavellian operator, Mendoza.

A filthy, tramp-like figure, with a music-hall comic's shimmying shuffle, Sher's Malevole launches into his reverse of a charm offensive with a rancid relish, savouring every diseased syllable of this character's voluble vision of man as "the slime of a dung pit" and of the world as the "very muckhill" on which the stars cast their excrement. He's particularly fine in his cagey little-and-large double act with Mendoza, who in Joe Dixon's deliciously funny performance is six and half feet of cigar-sucking machismo and misplaced sexual conceit.

Our interest in Altofront's possible restoration is weaker than our fascination with the depth of his alter ego's contempt for all earthly aspiration. This sense that most of the drama is Malevole's heightened perspective on reality was well conveyed in a production a few years ago which, in swapping male and female roles, tried to recapture the artifice and presumably compelling incongruities of the original Jacobean staging, where the twisted sex and violence were enacted by young boy performers.

There are no equivalent devices here where the 1970s' Latin American setting – courtiers done up like refugees from Saturday Night Fever; white-uniformed dictators appearing on balconies to adoring crowds – can raise awkward questions (a critic like Malevole surely wouldn't have lasted long in such a regime) and pose difficulties (as in the embarrassing final masque) when the play needs to enter and then sabotage a more formal mode. But the evening teems with theatrical life and the scabrous comedy of the court, with its suggestive Afro-wigged bawds (Claire Benedict) and its toupeed time-servers (the hilarious Geoffrey Freshwater), has just the right reek of cheap perfume. A vivid final touch to the Swan's wonderfully stimulating season of Jacobean rarities.

To 13 September (01789 403403)