It is a week since the tragic death of Philip Seymour Hoffman, whose sudden, premature absence from our film-going still does not bear thinking about.

Much has been written about how Hoffman was a character actor who became a star, someone who was not fast-tracked to fame by his looks but became pre-eminent through the depth and versatility of his work.

In contrast, Matthew McConaughey has taken a long time overcoming speedy success and the subsequent pigeon-holing that his Adonis-level handsomeness brought upon him. Early promise in films such as Richard Linklater's stoner comedy Dazed And Confused and John Sayles's Texas drama Lone Star gave way to a stream of forgettable romcom twaddle, such as The Wedding Planner and the aptly named Failure To Launch.

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McConaughey has spoken, graciously, of how he stepped back for a year until someone offered him something serious to work in. It paid off. Now he is beginning to show the danger, the range, the consistent acting chops that we expected from Hoffman. And after the creepy cop-cum-hitman of Killer Joe, the buff male stripper of Magic Mike, the good-natured escaped convict of Mud, and the epitome of poor role modeling in The Wolf Of Wall Street, comes the icing on the cake.

In Dallas Buyers Club, McConaughey plays Ron Woodroof, the real-life Texas electrician, rodeo cowboy and all-round bad apple who contracted HIV in 1985 and became - quite against character - a champion for the rights of Aids sufferers. When we first see Woodroof he is embroiled in a threesome during a rodeo, a clue to the sexual abandon that has made him prey to the HIV virus. He is 35, but looks 50, and unaware there is anything wrong with him.

Woodroof is not a nice guy. He is a hustler, a gambler and a typical Southern bigot. With his Stetson, shades and handlebar moustache, he would not be out of place in The Village People, but if you told him that he would probably knock you out. A minor work injury takes him into hospital. Once there he is quickly diagnosed, but refuses to believe it. The doctors give him 30 days to live. Woodroof's trailer-trash friends take no time in ostracising him, just as he would them.

He sets to reading about the virus in the library, and the moment that he finally accepts what is happened to him is, understandably, one of the film's most powerful moments. We now see a different Woodroof - the fighter, smart and resourceful, if still happy to break the law, using illicit means to wrangle a supply of the controversial AZT - the only drug approved for trials at that time. When AZT makes him worse, he investigates affordable, alternative treatments whose effects are infinitely better. He smells a business opportunity, and the buyers club is born.

If this was not a true story, one might condemn the contrivance. As it is, Woodroof really did take on the establishment that was pandering to the pharmaceutical companies, self-interest turned to a sort of civic duty, and the scoundrel became a likeable rogue, whose genuine friendship with Rayon (Jared Leto), a transsexual drug addict, gives the film its poignant heartbeat.

Leto's performance, like McConaughey's, is without affectation but deeply affecting. Yet we have seen Rayon before; Woodroof is a one-off. McConaughey shed 38lbs for the role, but the skeletal transformation would be nothing without the attitude - the caustic defiance, the humour, the incremental development of integrity in a man who would "prefer to die with my boots on".

With a story like this, served by a fine script, this may well have been a film worth watching anyway. But McConaughey makes it unmissable.