You can measure the mark that Harold Pinter has left on British theatre by one word: Pinteresque. Few playwrights get their own adjective. Barely any get one that communicates anything to the world at large. Yet the name Pinter summons up to almost anyone a pause-heavy world of veiled threats in ordinary rooms, of language as menace and menace as black comedy. You don’t even need to have seen The Homecoming or The Caretaker, No Man’s Land or Betrayal, The Birthday Party or The Dumb Waiter to have been affected by a playwright who changed British theatre for ever. Who plundered from naturalism and expressionism, from kitchen-sink realism and detective drama, and made from them something unmistakeably his own. Pinteresque, you might call it.

Was he really that great? Was he ever. People will always perform his plays for the same reason that they will always argue about his plays. They’re alive. They’re living, breathing, things. Yes, you can trace their roots – the literary-scene love triangle of Betrayal (1978), which might have been his most conventional play if he hadn’t told the story in reverse, came from his seven-year affair with Joan Bakewell in the 1960s. The Homecoming (1964) borrows from events in his Hackney upbringing; The Caretaker (1960) from his time in a house in Chiswick, West London. But he mixed realism with soaring acts of the imagination, however dowdy the setting. And that satisfying sense of closure, when you saw what a playwright was getting at and how he was getting there? Nope, you didn’t get that with Pinter. Even the shorter, blunter, more purposefully political work of his later years – the interrogation scenes of One for the Road (1984), the ruling elite back-slapping of Party Time (1991) – never stopped at finger-pointing. In implicating us all in the corruption of the political process, he stopped short of writing about them and us. And in blurring the lines between realism and fantasy – mixing conspirators with seaside boarding houses (The Birthday Party), basement-bound assassins with Eccles cakes (The Dumb Waiter), lovers’ vivid yet competing versions of events (Old Times) – he made his finely drawn dramas both strikingly modern and ineffably odd.

His early success came, haltingly, after John Osborne and Co had already changed the map. But Pinter’s linguistic exactitude made him a stronger flavour than Osborne or Wesker or other “angry young men”. He took the dull, how-was-your-day?, another-cup-of-tea? elements of drama and put them centre-stage, made them muscular, aggressive. Made them sing for their supper. And if he couldn’t do that, if he couldn’t make the practical pugilistic, or strategic, he’d cut straight to the chase. To the stuff that perplexes or bewitches. Does Ruth, the academic’s wife back from America in The Homecoming, really agree to go on the game for the family? Is that bad taste? Satire? A cop-out? One thing is for sure: it wasn’t realism, kitchen-sink or otherwise.

If you come at Pinter from the classroom, you may be ready for his weirdness, but not always his humour. His dark, claustrophobic battles of wills can also be incredibly funny. Because, in plays like No Man’s Land, he’s showing us the way men jostle and fight for space in every exchange, in every detail, and he’s showing us life. We’re pecking-order animals. And every glass of whisky, every lover, every favour, every joke, every question and every pause relates to that. The way that Pinter depicted language changed drama for good. No Beckett, no Pinter – but no Pinter, no Mamet; no Pinter, no Churchill, no Hare, no . . . it’d be easier to list the playwrights who aren’t influenced by him than the ones who are.

So will Pinteresque come to be a token of unabashed praise, in the way that, say, Shakespearean is? Well, there were many more commercially successful 20th-century playwrights than him – he never had bust-out success like Shaffer or Ayckbourn or even the intellectual yet accessible Stoppard. But he was, as I’m sure all those three would admit, a new breath for British drama in a way that nobody else could match since the war. He was a giant, a genius and a dab hand with a good one-liner. He was the greatest British playwright of the 20th century.

He wasn’t always easy. I once sat behind him at the theatre when a latecomer tried to climb past him to get to his seat. The rest of the row shifted for the latecomer. Pinter kept his legs thrust out, so the man had to climb laboriously over them. Tough, but funny. And as in life, so in art. The polite and not-so-polite pugilism he depicted is both quite unlike real life and also too much like it to bear. But his reputation, already great, will grow and grow – because the more you take away his plays from the times they appeared to be commenting on, the more you realise that they are timeless.

They’re not realistic. They’re so much better than that. They’re the truth.

Explore Stage

• Theatre

• Comedy

• Opera

• Dance

Editor's choice

• The 100 Best Films of the Decade
• 70 facts you didn't know about Marvel
• The 50 Biggest Movies Of 2010