Osborne, one of Britain's first and possibly fiercest "angry young men", died on Christmas Eve of a heart attack, aged 65. He earned the respect and hatred of a generation in 1956 with his debut play, Look Back In Anger, which broke the mould of contemporary theatre and ushered in the the era of the gritty kitchen sink drama.
The dramatist Howard Brenton, some 15 years younger than Osborne and described by him as a "hairy armpit writer", praised his non-conformity.
"He was totally unknightable. There was no way he could be assimilated or taken to the Commons. He was such a difficult old bugger but quite charming when you met him," Brenton said.
"Look Back In Anger was electric at the time. When somebody breaks the mould so comprehensively it's difficult to describe what it feels like. It's the same way the younger generation is knocked over by Tarrantino [Quentin, script writer and film director]."
The dramatist Arnold Wesker, a contemporary and friend of Osborne's, said that he "opened the doors of theatre for all the succeeding generations of writers".
"His greatest contribution is to have brought a fierce intensity of passion to the stage. Very few writers had quite his depth of feeling," he said.
Wesker said that Look Back in Anger should not be understood so much for its anger but as a passionate plea for old-fashioned values of loyalty and friendship. "What John cared about was basic human values," he said.
But there was a darker side to his nature, he added. Osborne regularly lashed out at anyone who annoyed him. Chief targets for abuse included his fourth wife, the actress Jill Bennett - whose suicide he called the "coarse posturing of an overheated housemaid". After her death he said that his chief regret was his inability to "look down upon her coffin and drop a large mess in her eye". He had also publicly attacked his teenage daughter for being "insolently smug . . . devotedly suburban".
As a result, Wesker said: "There will be a lot of nonsense talked about him and there will be a lot of people who will get their sour revenges. But when all this is over I hope it will all be put in perspective."
The writer Hunter Davies, who interviewed Osborne for the Independent earlier this year, said he "had this image of being tough and cantankerous, but in reality he was far tougher on himself".
"He had done his best work, but its always a blow when somebody who breaks the mould dies. It's also a blow for literature because he was emerging as a brilliant biographer," he said.
"He was actually very funny. He had a badge in his bathroom which said `Since I gave up hope I feel much better'. And he had a cushion which had written on it `Eat, drink and remarry."
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