Pete Postlethwaite, who died of cancer aged 64 on Sunday, has been called the “best actor in the world” by Steven Spielberg and is remembered as a both an acting genius and a political activist.

Postlethwaite was a household name in Britain after starring in films like Brassed Off, In The name Of The Father and The Usual Suspects. It was after working with Spielberg on Jurassic Park that Postlethwaite was described as “probably the best actor in the world” by the director.

However it was his modesty and lack of ego which endeared Postlethwaite to his fans and when asked about the accolade his response was: “What he [Spielberg] actually said was that Pete thinks he’s the best actor in the world.”

Postlethwaite began his acting career at Bristol’s Old Vic theatre where he worked and befriended Daniel Day-Lewis. He spent some time at Liverpool’s Everyman Theatre, acting with the likes of Julie Walters, Bill Nighy, Jonathan Pryce and Alan Bleasdale.

Walters, who began a five-year relationship with Postlethwaite in the 1970s, said: “He was quite simply the most exciting, exhilarating actor of his generation. He invented ‘edgy’. Spielberg was right when he said he was the best actor in the world.”

In the 1980s Postlethwaite moved from the Royal Shakespeare Company to work in TV and by the 1990s he was in Hollywood with major roles in Hamlet in Alien 3.

In 1993, Postlethwaite played Guiseppe Conlon in Jim Sheridan’s Guildford Four film, In The Name Of The Father, and received an Oscar nomination for the role depicting the wrongly imprisoned man accused of an IRA bomb attack.

Gerry Conlon, who was played in the film by Day-Lewis, told Sky News that Postlethwaite got the role of his father “so right”.

Day-Lewis said of working with Postlethwaite: “Pos was the one. As students it was him we went to see on stage time and time again.

“He shouldn’t have gone. I wish so much he hadn’t. There’s a tendency to make lists at this time of the year. When we get to the Best of British if Pete isn’t at the top of that list he shouldn’t be far from it.”

Kevin Spacey, who starred with Postlethwaite in The Usual Suspects, also paid his respects to the beloved actor.

“He was a great man of the theatre as well and carved a unique life for himself in film. He probably wasn’t appreciated as much as he should have been, but I suspect that the country will come to regard him as a national treasure.

“For the rest of the world he was a guy we could all understand, empathise with and be frightened by. We will all treasure his performances and remember him with fondness and enormous admiration.”

Postlethwaite was a lifelong political activist who in recent years marched against the war in Iraq and starred in The Age of Stupid, the 2009 film about global warming.

Postlethwaite died in hospital in Shropshire on Sunday after a long battle with cancer. He continued to work until months before his death.