Daniel Radcliffe, who played the boy wizard in the blockbuster Potter series, led the tributes to a man he said had offered him "encouragement, tutelage and humour". The two men worked together on the films and later in the play . "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 was born on July 31, 1947 in Yorkshire, northern England, the son of a steelworker. His parents were deaf, so he learned sign language at an early age. He left school at 15 and worked as a porter, but his boss persuaded him to go back to education to study drama. He later joined the Royal Shakespeare Company, excelling in playing the clown.

Early film credits included , and , before he landed a starring role in the 1987 comedy . Griffiths played the eccentric gay uncle of Withnail, an out-of-work, alcoholic actor played by Richard E. Grant, in a film regarded as a British classic. Grant said on Twitter: "My beloved 'Uncle Monty' … died last night. Chin-chin my dear friend."

Nicholas Hytner, director of London's National Theatre who directed Griffiths in one of his biggest stage hits, , said he was "the life of every party". He recalled anecdotes that "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".

Griffiths won a Tony and an Olivier award for his role as an inspirational teacher in , and was nominated for a Bafta for the film version. "His performance in was quite overwhelming: a masterpiece of wit, delicacy, mischief and desolation, often simultaneously," said Hytner.

As a stage actor, Griffiths demanded his audience's full attention, having twice stopped a show to order people out of the theatre after their mobile telephones rang out. He also had a successful television career, starring as a crime-solving chef in the series in the 1990s, and he was awarded an OBE for services to drama in 2007.