Richard Griffiths, the award-winning actor famous for his roles in Withnail & I and Harry Potter, has died following complications after heart surgery. The celebrated stage and screen star, one of Britain's best-known character actors, was 65.

Tributes poured in for the actor, who died on Thursday at the University Hospital of Coventry and Warwickshire. Daniel Radcliffe, who starred alongside Griffiths in the Harry Potter films, said the actor made any room "twice as funny".

Radcliffe said Griffiths had supported him at two key points in his career, when he first played the young Harry Potter and later when he made his stage debut in Equus.

"In August 2000, before official production had even begun on Potter, we filmed a shot outside the Dursleys', which was my first ever shot as Harry. I was nervous and he made me feel at ease," he said.

"Seven years later we embarked on Equus together. It was my first time doing a play but, terrified as I was, his encouragement, tutelage and humour made it a joy. In fact, any room he walked into was made twice as funny and twice as clever just by his presence. I am proud to say I knew him."

Richard E Grant, who played the title role in Withnail & I, paid tribute to his late co-star on Twitter. He wrote: "My beloved 'Uncle Monty' Richard Griffiths died last night. Chin-Chin my dear friend."

Griffiths was feted for his roles as Withnail's eccentric Uncle Monty in the cult classic and Hector, the unconventional teacher in Alan Bennett's play The History Boys, for which he won the Laurence Olivier Award for best actor, the Drama Desk Award for outstanding actor in a play, the Outer Critics Circle Award for best featured actor in a play, and a Tony Award for best performance by a leading actor in a play.

He gained widespread fame as grumpy Uncle Vernon in the Harry Potter films and was much loved as disillusioned police officer and pie chef, Inspector Henry Crabbe, in the successful TV detective drama series Pie In The Sky.

Sir Nicholas Hytner, director of the National Theatre, said Griffiths' "army of friends" would be devastated by his unexpected death. "Richard Griffiths wasn't only one of the most loved and recognisable British actors – he was also one of the very greatest," he said.

"His performance in The History Boys was quite overwhelming: a masterpiece of wit, delicacy, mischief and desolation, often simultaneously. But that was just one small part of a career that spanned Shakespeare, cutting-edge new plays and major work in film and television."

Hytner, who directed Griffiths in The History Boys and The Habit Of Art, added: "His currency as an actor was truth; as a colleague it was hilarity. His anecdotes were legendary. They were, literally, endless. They would go on for hours, apparently without destination, constantly side-splitting.

"The only way to stop them was to tell him you were walking away, though there were always others in the audience so, as far as I know, he never stopped. He was the life of every party."

Thea Sharrock, who directed Griffiths in Equus, Heroes and Sunshine Boys, said: "I worked with Richard more times than any other actor. Everybody knew he was my favourite. He was the most tender, gentle, kind, generous, loving man. His curiosity was unending, as was his striving for perfection. I cannot imagine a world without all those stories. I will miss him so very, very much."

The producers of Heroes and Equus, David Pugh and Dafydd Rogers, said the actor was a "great man, a great character, a great talent greatly missed".

Griffiths, the son of a steelworker, was born in Thornaby-on-Tees, North Yorkshire, in 1947 were he cared for his deaf parents. He left school at 15 but later studied drama, before joining the Royal Shakespeare Company. He married Heather Gibson in 1980 after they met during a production of Lady Windermere's Fan in 1973.

His portly stature, which made him instantly recognisable on screen, was thought to have been caused by medication he was given as a youngster. He was awarded an OBE for services to drama in 2007.

His agent, Simon Beresford, said his thoughts were with Griffiths' wife and family. "Richard brightened my days and enriched the life of anyone he came into contact with. On stage he allowed us to share in our own humanity and constantly question our differences," he said.

"Richard gave acting a good name. He was a remarkable man and one of our greatest and best-loved actors. He will be greatly missed."