LONDON >> Richard Griffiths was one of the great British stage actors of his generation, a heavy man with a light touch, whether in Shakespeare or Neil Simon. But for millions of movie fans, he will always be grumpy Uncle Vernon, the least magical of characters in the fantastical "Harry Potter" movies.

Griffiths died Thursday at University Hospital in Coventry, central England from complications following heart surgery, his agent, Simon Beresford, said. He was 65.

"Harry Potter" star Daniel Radcliffe paid tribute to the actor Friday, saying that "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," Radcliffe said.

Griffiths won a Tony Award for "The History Boys" and appeared in dozens of movies and TV shows. But he will be most widely remembered as a pair of contrasting uncles — Harry Potter’s Uncle Vernon Dursley and Uncle Monty in cult film "Withnail and I."

Griffiths was among a huge roster of British acting talent to appear in the "Harry Potter" series of films released between 2001 and 2011.

His role, as the grudging, magic-fearing guardian of orphaned wizard Harry, was small but pivotal. Griffiths once said he liked playing Uncle Vernon "because that gives me a license to be horrible to kids."

But Radcliffe recalled Griffiths’ kindness to the young star.

"Richard was by my side during two of the most important moments of my career," said Radcliffe, who in 2007 starred with Griffiths in a London and Broadway production of "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.

"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 humor made it a joy."

Earlier, Griffiths was the louche, lecherous Uncle Monty to Richard E. Grant’s character Withnail in "Withnail and I," a low-budget British comedy about two out-of-work actors that has become a cult classic. Years after its 1987 release, Griffiths said people would regularly shout Monty’s most famous lines at him in the street.

"My beloved ‘Uncle Monty’ Richard Griffiths died last night," Grant tweeted Friday. "Chin-Chin my dear friend."

A huge stage presence — through charisma as well as obesity — Griffiths created roles including the charismatic teacher Hector at the emotional heart of Alan Bennett’s school drama "The History Boys." He won an Olivier Award for the part in London and a Tony for the Broadway run, and repeated his performance in the 2006 film adaptation.

National Theatre artistic director Nicholas Hytner, who directed "The History Boys," called Griffiths’ performance in that play "a masterpiece of wit, delicacy, mischief and desolation, often simultaneously."

Griffiths also played poet W.H. Auden in Bennett’s "The Habit of Art," a hugely persuasive performance despite the lack of physical resemblance between the two men.

Griffiths was born in northeast England’s Thormaby-on-Tees in 1947 to parents who were deaf and mute — an experience he and his directors felt contributed to his exceptional ability to listen and to communicate physically.

"The first language he learned was sign. And therefore his ability to listen to people with his eyes as well as his ears is incredible," Thea Sharrock, who directed "Equus," told The Associated Press in 2008.

Griffiths left school at 15 but later studied drama and spent a decade with the Royal Shakespeare Company, making a specialty of comic parts such as the buffoonish knight Falstaff.

On television, he played a crime-solving chef in 1990s’ British TV series "Pie in the Sky," and he had parts in movies ranging from historical dramas "Chariots of Fire" and "Gandhi" to slapstick farce "The Naked Gun 2 ½."

Known for his sense of humor, large store of rambling theatrical anecdotes and occasional bursts of temper, Griffiths was renowned for shaming audience members whose cell phones rang during plays by stopping the performance and ordering the offender to leave.

Griffiths’ last major stage role was in a West End production of Neil Simon’s comedy "The Sunshine Boys" last year opposite Danny DeVito. The pair had been due to reprise their roles in Los Angeles later this year.

Griffiths is survived by his wife, Heather Gibson.