LOS ANGELES (Reuters/AFP) - The award-winning British playwright Sir Peter Shaffer, best known for penning Amadeus and Equus, died on Monday in County Cork, Ireland, of pneumonia and age-related issues, his long-time agent said. He was 90.

Shaffer died at a hospital . He was surrounded by friends and family at the time of his death, just a few weeks after his 90th birthday, agent Dennis Aspland told Reuters.

Born in Liverpool, and educated in London and Cambridge, he established his career with 1954's The Salt Land,produced for BBC television, and comedies such as The Private Ear and The Public Eye, both starring Dame Maggie Smith.

Shaffer was nominated for an Oscar in 1978 for his screenplay for Equus, his 1973 stage play about a psychiatrist treating a young man fascinated by horses.

On Broadway, it opened in 1974 with Anthony Hopkins and Peter Firth as the stars. It won numerous awards in 1975, including the Tony Award for best play, as did his drama Amadeus in 1981.

Richard Burton starred in the 1977 film version of Equus, directed by Sidney Lumet. It enjoyed a 2008 Broadway revival which starred Richard Griffiths and Daniel Radcliffe.

Shaffer won the Oscar in 1985 for the adaptation of Amadeus, his drama about composer Antonio Salieri's jealous fixation with Wolfgang Amadeus Mozart. It was one of eight Oscars which the film won that year.

Amadeus will be revived at London's National Theatre, which Shaffer was closely involved with, this fall.

The playwright was awarded the Commander of the Order of the British Empire (CBE) in 1987 and was knighted in 2001 by Queen Elizabeth II.

He is survived by his brother, Brian Shaffer. Peter Shaffer was the twin of Anthony Shaffer, the screenwriter and playwright whose screenplays included the Alfred Hitchcock film Frenzy, the British cult thriller movie The Wicker Man and Agatha Christie's Death On The Nile. Anthony Shaffer died in 2001.