A character actor who briefly became a star in 1984, appearing in leading roles in Paris, Texas and Repo Man, Harry Dean Stanton (born in Kentucky in 1926) was also part of what made the seventies such a great decade for film, a time when character actors had the heft of leading parts but happened to play on the margins of a movie rather than at its centre. In Sophie Huber's Harry Dean Stanton: Partly Fiction, writer and actor Sam Shepard talks of the actor's reservations about playing the main role in Paris, Texas. Yet Shepard couldn't see any reason why Stanton couldn't master the role: it is just a character actor getting a bigger part. Shepard has a point but maybe for many actors this wouldn't have been so, since film often practices a variation on what the novelist EM Forster calls round and flat characters. Round characters have subtlety, nuance and depth, but 'flat characters were called "humours" in the seventeenth century, and are sometimes called types, and sometimes caricatures. In their purest form, they are constructed round a single idea or quality; when there is more than one factor in them, we get the beginning of the curve towards the round.'

Stanton was in this sense always a round character actor, and through the seventies appeared in Two-Lane Blacktop, Pat Garrett & Billy the Kid, Cockfighter, The Missouri Breaks, 92 in the Shade, Renaldo and Clara, Straight Time and Alien. He was someone that could play a small role without it feeling no more than a plot function, and Huber's documentary shows a scene from The Missouri Breaks illustrating this well. As his horse rustler talks to Jack Nicholson about his past, director Arthur Penn films Stanton's brief revelation in a single take. Talking about his father's cruelty and his own revenge, Stanton delivers his lines with the force of a leading man's back story, though it remains merely the anecdote of a supporting player.

Stanton can be flippant about his interest in cinema, talking about the theatre being too damn demanding and money and girls more easily acquired through film, but his personal assistant insists that Stanton works so hard on the material he can remember other characters' lines and not just his own. When David Lynch says in the film that many actors can memorize their lines, but what they can't do is take care of their silences, Stanton seems someone who manages to memorize his and the other characters' and take care of the silences too. This is beautifully illustrated in a clip from Lynch's The Straight Story. As Stanton looks out at the motorised lawnmower his estranged brother has driven 240 miles in to visit him, so the emotion becomes too much. It might be Richard Farnsworth who has the leading role, but in this moment it is Stanton who has what we might call the 'leading feeling'.

Stanton understands the years of silence that can yawn between people, and knows that dialogue is sometimes just a bridge to cross it. Much of the time in Huber's doc, Stanton, a frail, melancholic figure, is happier singing a song about pain rather than expressing his own too directly, as if words ought to be used only when we can put meaningful feelings into them. As Wim Wenders notes in the film, Stanton has always been a vulnerable, sensitive man; it's a point also made by an acquaintance of Stanton's who has known him since the late 60s. Stanton doesn't talk much but what he says really matters, the friend says, and this is no doubt partly what makes Stanton such a marvellous supporting player. He might have over his many years in film been given relatively few lines, but he knows that the feeling often lies elsewhere anyway.

Harry Dean Stanton: Partly Fiction showed at the Edinburgh International Film Festival 2013.

Harry Dean Stanton: Partly Fiction | Official Trailer