For actors, physical type is often destiny: height, weight, hairline and colouring can all dictate whether they will play romantic leads, comic foils or villains. Burly and with a good line in surly looks – and with Italian-American heritage as well – James Gandolfini was always at risk of being stereotyped as a mobster or a heavy.

What was remarkable about The Sopranos, though, was that Gandolfini – and David Chase, creator of the HBO series, which ran between 1999 and 2007 – took a dramatic type that had become familiar in American popular culture, through The Godfather films and Goodfellas and other examples, and made it completely their own. They managed this despite the fact that even the variation on the Mafioso bloke that Gandolfini's Tony Soprano represented – the gangster with neurotic doubts about his calling and his killing – already had a predecessor in the nervy murderer played by Robert De Niro in the movies Analyze This and Analyze That.

One advantage Chase and Gandolfini had, though, was that a long-form TV series permits the protagonist to be developed and challenged at a depth impossible in a film, play or novel. Chase saw in the TV serial the possibility for a sort of visual novel equivalent to thousands of pages. In his 80 or so hours of screen-time as he head of a New Jersey crime family, the actor was able to display every facet of the complex character of a man who was professionally and genetically required to be a wolf but, underneath, had deep fears and dreams of being a pussycat.

James Gandolfini as Tony Soprano: 'surprising gentleness, as if frightened of his own potential strength'. Photograph: Sportsphoto Ltd/Allstar/HBO

To carry such a concentration on a single figure – other great modern American TV shows such as The Wire, The West Wing and Six Feet Under were all ensemble pieces – Chase needed a remarkable actor – and he got one.

All the best TV actors – from Alec Guinness through Helen Mirren and David Suchet to Benedict Cumberbatch – have had two predominant skills: stillness and thinking. A small-screen role is defined in moments of repose, when the camera stops and watches. Because Tony Soprano was often sitting, in long consultations with his shrink or with family or associates over a meal, and was frequently unable to speak the truth, the part demanded above all the ability to suggest the mental activity churning within physical inactivity.

Gandolfini could convey multitudes with a look: whether baleful, lecherous, menacing, halfsmiling, impassive. Through this flexibility of expressions, he indicated the guilt, memories, regrets and desires that enfolded Tony. And, as is often the case with big men, he often moved with surprising gentleness, as if frightened of his own potential strength, an effect intensified by a vocal range that could encompass softness as well as the growl his stature led you to expect.

But, while his character was often cornered or tortured, Gandolfini also had to make it credible that this was a man who had killed for a living. The actor carried a rare sense of danger and rage that was controlled, at least for the moment. His explosion of anger in the Broadway production of Christopher Hampton's translation of Yasmina Reza's play The God of Carnage remains one of the most terrifying spectacles I have ever seen on stage.

The Sopranos was part of a wave of American TV dramas that finally persuaded cineastes and critics who had been snobbish and dismissive about television as a medium to accept the smaller screen as an artistic equivalent of the larger one. Although many of those who watched and wrote about TV had got this message much earlier, the remarkable and sustained range of Gandolfini's portrayal of Tony Soprano played a major part in ending any remaining inferiority complex about the medium.

Busy in movies on either side of The Sopranos, the actor did relatively little other TV work, although he had recently signed up to return to HBO in the American version of Peter Moffat's British legal series, Criminal Justice. There had long been talk of a possible Sopranos sequel – left possible by the ambiguous final shoot-out scene – which would probably have been made for cinema.

That possibility dies with Gandolfini and it may be right that Tony Soprano will now remain forever a character of television, a form in which he represents one of the greatest achievements. It is a small consolation for his shockingly early loss that TV now has such a considerable after-life on archive channels and through box-sets.