He could, though. His dreamy impassivity was at the centre of a few truly great films noirs, his psychopathic preacher in Night of the Hunter (1955) may be the most compelling study of evil in cinema, and he nearly saved David Lean's overblown Ryan's Daughter, dammit.
When Mitchum played Philip Marlowe in 1975 he was ridiculously old for the part at 58, but his world-weary cynicism and amused detachment still seemed to capture Chandler's detective far more effectively than Bogart's more famous portrayal in the Forties.
Maybe Mitchum was Keaton to Bogart's Chaplin. The more showy performer won the accolades but Mitchum's was the art that conceals art, and has lasted better.
Nobody contributed more to concealing his art than Mitchum himself. "Listen. I got three expressions," he said, "Looking left, looking right and looking straight ahead." Of his famous walk which, with his unfeasibly broad shoulders and hips, resembled a wardrobe sliding into the room on castors, he said: "Hell, I'm just trying to hold my gut in."
Self-deprecation has always been part of the actor's stock-in-trade, usually so we can tell the performer how wonderful he really is. But in Mitchum's case we can assume it was sincere. This is a man who went to California as a writer but switched to acting when he found you could earn more money for less effort.
Not that he wasn't prepared to work hard when it was needed. Director John Huston described him as "a rarity among actors, hard-working, non- complaining, amazingly perceptive, one of the most underrated stars in the business."
While this much-admired work was being done, Mitchum was a regular subject of "booze, broads and brawls" stories in the Hollywood gossip sheets. His scrapes included two months in prison for "smoking a marijuana cigarette", quite shocking in 1948, and allegations in Confidential magazine that he had stripped off at a fancy dress party, doused himself in ketchup and announced that he was a hamburger. Mitchum denied the story, but the point is, they wouldn't have made it up about Laurence Olivier.
Another essential difference between Mitchum and Sir Laurence Olivier was the former's little-known addiction to calypso music. While filming in the West Indies in 1956 Mitchum, when not relaxing in the more publicised ways detailed above, liked to pick up his guitar and mimic the local music. A year later he met a Capitol record executive in the Beverly Hills Hotel and played him a calypso he had written. The result was a bizarre album called Calypso Is Like So...
Mitchum himself would clearly never have thought any of his behaviour particularly heroic, but for the slacker generation, and hippies and beatniks before them, a man whose cultural baggage could include both Charles Laughton and Dick Dale, and who seemed to be able to turn up for work with a hip flask in his pocket, a spliff behind his ear, and a starlet on either arm and still make films like Out of the Past (47) or Angel Face (52), has to be something of a hero.
What made Mitchum particularly admirable is that, dedicated though he was to fun, fun, fun ("I started out to be a sex fiend," he said, "but couldn't pass the physical"), he never missed a gig. A hundred and thirteen films, some of them irredeemably awful, but Mitchum always defiantly Mitchum. As David Lean said, "Mitchum can, simply by being there, make almost any other actor look like a hole in the screen."