In `Backlash', the late JT Walsh yet again gave a brilliant performance in an `ethically challenged' role. Ryan Gilbey celebrates a talent never fully recognised
Where were you when you found out that JT Walsh had died? Even those readers who didn't answer "JT Who?" may not even have known that he was dead until a moment ago. Walsh belonged to a species which is at once instantly recognisable and consigned to near-obscurity - the character actor. A successful one can make an entire film click without you even realising what he's doing. In return, you will always know his face while his name is doomed to languish forever on the tip of your tongue.

Walsh, who died in February, aged 54, of a heart attack, was the finest character actor of modern cinema. He had come to acting relatively late in life, making the leap from nine-to-five work to off-Broadway shows in 1974 at the age of 30.

Early on, he cemented a relationship with the playwright David Mamet which was to prove highly profitable - he won a part in the first run of Mamet's American Buffalo in 1976 and really made waves eight years later on Broadway as Williamson, the boss and tormentor of the sales team, in Glengarry Glen Ross.

Walsh quickly became part of Mamet's unofficial repertory of favoured actors, and when the writer ventured into directing films with House of Games, he chose Walsh to play a shifty master conman. Walsh's performance had the electrifying zing that only comes with perfect casting, and the role demanded the very traits that were to become Walsh's speciality: insidiously bullying persuasiveness and intractable moral corruption.

It was a part that fitted Walsh as snugly as a cat-burglar's glove. He played another genius of the long con in Stephen Frears' The Grifters, in which a character describes him as "so crooked that he could eat soup with a corkscrew".

In his final scene, he undergoes a disturbing mental breakdown, displaying a savagely vulnerable side which, frustratingly, he rarely got the chance to expose - if Cassavetes had ever got hold of him, the resulting footage would surely have combusted in the projector.

But you never got the impression that his talents were being squandered. Stephen Frears has spoken of Walsh's "plain man's hunger to get the most out of his scenes", and in every role, however brief, you can feel him inhabiting each pore of a character the way tear-gas permeates a room.

While he played scam kings in House of Games and The Grifters, he was the scum king in most of his other films. The sweaty bartender plotting his wife's murder in John Dahl's Red Rock West. A man driven to violence by a backlog of parking tickets in Needful Things. A lecherous, booze- soaked father pestering Alicia Silverstone in the little-seen The Babysitter. And in the industry satire The Big Picture, he was appallingly funny as the studio executive who imposes his own sexual preferences on every project that he green-lights. Walsh employed a neat euphemism when describing these characters: he called them "ethically challenged".

Where many character actors run the risk of having their creativity suffocated by typecasting, Walsh cleverly used his familiarity to his advantage. Directors kept returning to him: Mamet (Things Change), Dahl (The Last Seduction), Barry Levinson (Good Morning Vietnam, Tin Men).

He accumulated an impressive body of work in which he explored the persona of the venal, predatory but ultimately frustrated middle-aged male. The fact that he returned to this territory over a 14-year period often distracted from the fact that his work was executed with the concentrated intensity of a De Niro or a Depardieu, vindicating Robert Altman's argument that actors should be regarded as auteurs. In his choice of parts, Walsh proved his commitment to exploring the depths of cancerous souls, as though he were dragging a lake, searching for corpses.

Walsh's performance in the new thriller Breakdown wasn't his last. Frears has said: "I doubt he ever had more than a few days out of work."

And, true to form, there are at least three more of Walsh's films currently awaiting release, including the award-winning Sling Blade, in which he plays a mental patient.

But Breakdown conveniently encapsulates everything that was great about Walsh - everything that made him worth 10 Matt Damons, 20 DiCaprios. For all the despicable acts that Walsh's psychopathic truck driver performs during the movie, the most distressing point comes when we meet his wife and child: he's a wolf in a family man's clothing.

This moment embodies the Walsh menace. He had a knack for revealing the monster within the travelling salesman, the working stiff, the Ordinary Joe. When you looked into his eyes, you were confronted by that with which you could not reason: the implacable logic of a scrupulously intelligent man who has considered every possible route in life before choosing the most amoral one. That's what I call frightening.