Heath Ledger: We only had a glimpse of what might have been...

Named after Emily Brontë's brooding hero in Wuthering Heights, Heath Ledger should and could have built a lucrative career as a Hollywood heartthrob. He had those immensely likeable, open-faced good looks: the looks of a carefree, sun-kissed surfer-dude, a type he has played in films such as Lords of Dogtown. He seemed perfectly equipped to carry light comedies and rollicking action adventures, and had his share of them.

Yet Ledger was also beginning to emerge as an old soul, in the most positive of senses: a man who could conjure a pent-up complexity and gravity beyond his years. It's a rare ability. His generation of American actors is lamentably short on top-flight leading men who can open a movie on a Friday night but also deliver a superb performance. Ledger stood virtually alone among his peers in his ability to combine magnetic star quality with a grand emotional range. By the time he died this week, aged 28, he seemed to be heading for greatness.

After modest beginnings in Australia – including a stint in Home and Away – Ledger's international breakthrough came in 10 Things I Hate About You. It attracted great reviews for its freshness, as did Ledger for his goofy bad-boy.

He was picked by Mel Gibson to play the latter's idealistic son in The Patriot, a bloody revenge drama set against the backdrop of the American Revolution, and squared off convincingly against the elder Australian. The boisterous rock'*'roll A Knight's Tale cast him as a rebel outsider, an impudent squire who passes himself off as a knight in armour, and though the film was nugatory, the actor made an attractive impression as a medieval sports jock. He played yet another swaggering outlaw in Ned Kelly.

But Ledger was beginning to branch out. He seemed drawn to troubled characters: he had a sharply etched supporting role in Monster's Ball as the unhappy prison guard who shoots himself in front of his father, and played a smooth-talking heroin addict spinning out of control in Candy. However, Ledger was still landing romantic leads. In Lasse Hallstrom's revisionist Casanova, he played the title character as a womaniser caught up in a high-spirited costume farce; and although the reviews were mixed to dismissive, he brought a sexiness and dash to the character that did no harm to his reputation.

In fact, 2005 was a banner year for Ledger with starring roles in three high-profile movies in competition in Venice. He played one of Terry Gilliam's Brothers Grimm, in a Pythonesque period romp that imagined the siblings as con-artists. Once again, the film was disappointing. But Ledger's third Venice appearance transformed his image, gave him his first and, tragically, his only unquestionably great role and served definitive notice of a major-league talent.

That film was Brokeback Mountain. Ledger played Ennis, a handsome, lonesome cowboy anguished and undone by his gay sexuality, taking the character from a strong-but-silent ranch hand to a bewildered, broken old man. It was a role in which everything was expressed between the lines: a scene near the end of the story in which, with sad rheumy eyes, Ennis caresses the shirts of his dead lover (Jake Gyllenhaal) is a quietly heartbreaking image of love lost. Ledger's intense performance earned him an Oscar nomination and had many, including the film's director, Ang Lee, comparing him to a young Brando.

He was famously fussy about his roles and, although he worked steadily, could scarcely be called prolific. But we haven't quite seen the last of him. He can be seen in Todd Haynes's eccentric Bob Dylan biopic, I'm Not There, as one of six actors playing facets of the singer. Ledger's character is the least attractive, a vain, sulking, self-absorbed star who neglects and disrespects his wife (Charlotte Gainsbourg) and children to chase fame and wallow in affairs. In spite of all that, Ledger's charm and charisma made him – along with Cate Blanchett – by far the most memorable of the Dylans. Yet, in one of the last interviews he gave, to The New York Times, he conveyed the impression of a troubled, restless soul, full of self-doubt and more and more ill-at-ease with his spiralling celebrity. He had, he admitted, difficulty sleeping, despite resorting to pills. Photographs showed him tired, drawn, and looking older than his years.

I'm Not There may be his last fine performance – but there is still one surprise in store. Ledger stepped into Jack Nicholson's shoes to play The Joker in the forthcoming Batman movie, The Dark Knight, whose marketing will now be tricky. He had also begun shooting another film with Gilliam, a theatrical fantasy called The Imaginarium of Doctor Parnassus.

Ledger's was a frustrating, tantalising career – studded with films unworthy of his gifts, but also with fine achievements and the glittering promise of what might-have-been. He took his work with the utmost seriousness and invested his all in a character, to his own detriment if recent reports are to be believed. Yet there was an apparent effortlessness to his performances, and a lack of actorly mannerisms. This was never work that stridently demanded we pay attention.

Perhaps the most striking thing is the versatility of his range. Ledger seemed at ease as a romantic lead, a light comedian, an action hero or in a harrowing dramatic role. He was impossible to typecast and it's difficult to single out his four best films: Brokeback Mountain earned him recognition and the acclaim of his peers. But his appearances in 10 Things I Hate About You or The Patriot, Candy or Casanova, have their equally fervent admirers.

His potential was very far from exhausted. But Ledger has taken his place in that grim Peter Pan pantheon of legends cut down in their prime. The film world is immeasurably the poorer.

A life in pictures

Brokeback Mountain

Ledger was warned that playing a closet-gay cowboy amounted to career suicide. In the event it was the role of his lifetime – and one that gives us a poignant vision of how he might have grown old. Incidentally, if one wanted a definition what sets aside a star from an accomplished jobbing actor, one need look no further than the difference between Ledger's performance and that of his screen lover and co-star, Jake Gyllenhaal.

A Knight's Tale

Perhaps this silly medieval rock-pic will not stand the test of time as one of Ledger's finest movies. It is none the less a guilty pleasure to behold him as the cheeky squire who passes himself off as a knight; indeed, the general silliness of the conceit proves his ability to carry off a mediocre movie with charm and chutzpah.

10 Things I Hate About You

The Taming of the Shrew must be one of the hardest plays in the Shakespeare canon to update to a modern setting. But, as American high-school teenagers, Ledger and his co-star, Julia Stiles, bring an irrepressible jollity and sunny sexual chemistry to the party as, respectively, the rebel with a dodgy past and the swot with whom he falls in love.

I'm Not There

In this unconventional Bob Dylan biopic, Ledger is one of six actors playing loosely fictionalised versions of the singer at various phases of his early career, incarnating the singer just as he was breaking through as a movie star in the Seventies. It comes across an arresting, perversely magnetic portrait.