On 3 August 1966, radical comedian Lenny Bruce was found dead in the bathroom of his Los Angeles home - the victim of a drug overdose.

The 40-year-old had revolutionised stand-up comedy, leaving an impact on the art form that endures 40 years after his death, but his career was eventually destroyed by battles with the US justice system.

In his final years, Bruce found himself in virtual professional exile, with almost every nightclub in the US fearing prosecution and blacklisting him following his 1964 conviction for obscenity.

When he did perform in the latter stages of his career, Bruce frequently alienated audiences by simply reading transcripts from the legal battles over freedom of speech with which he had become obsessed.

It was a tragic decline for a man who had had a seismic impact on the industry, with highly improvised and personal shows that offered lacerating social commentary and wilfully demolished taboos surrounding topics like politics, religion, racism, sex and drugs.

Pioneer

"Lenny Bruce's legacy is freedom of speech and telling it as it is, getting your life and putting it out on the table, telling everyone about it," comedian and actor Eddie Izzard told BBC Radio Two's documentary Lenny Bruce is Dead.

"I think he was the first one to do it as an individual, and we've all followed that."

Australian comedian Brendon Burns agrees: "Without Lenny Bruce a lot of us wouldn't be able to do what we do today."

He pioneered stand-up about things "everyone does and everyone thinks, but it just wasn't polite to talk about", Burns told BBC News.

"He was bringing it from behind closed doors - and that's pretty much what a lot of stand-up is now."

In 2004, US cable channel Comedy Central named Bruce the third greatest stand-up of all time, behind fellow Americans Richard Pryor and George Carlin - both of whom cite Bruce as an influence.

"He changed everything," says Burns.

"He turned comedy into a freedom of speech art form. And everyone else then went and changed everything they did off the back of him."

American comedian Dick Gregory, who started out at about the same time as Bruce, says: "If you could be in the audience when he came up with that 45 minutes to an hour's worth of genius, you knew you had been blessed.

"America has produced three comedic geniuses - Mark Twain, Lenny Bruce and Richard Pryor - and what Lenny was doing back then frightened people."

Martyr

Burns has a reputation himself for shocking audiences and says that the worst consequence today is that certain clubs refuse to book him.

"I say what I like, but no-one is arresting me," he says.

Bruce's unprecedented provocative material, not to mention his frequent use of expletives, drew the authorities' attention and led to repeated arrests and his eventual conviction for obscenity.

He apparently could not comprehend such a reaction to mere words, reportedly saying to police at the time of one arrest: "I didn't do it, man, I only said it."

His professional decline and premature death have led to him being deified as a martyr of free speech - Izzard has called him "the Jesus Christ of alternative stand-up".

Record producer Phil Spector printed in Billboard magazine an announcement following Bruce's death that read: "America's foremost, and certainly most truthful, philosopher died from an overdose of police."

Burns says: "I think there was probably some romanticism around the 'martyrdom', but the fact of the matter is that it was martyrdom nonetheless."

Playboy magazine's obituary included the now-famous last line: "Finally, one last four-letter word concerning Lenny Bruce: Dead. At forty. That's obscene."

Cultural impact

It is arguable that Bruce is now better remembered for his demise than for anything funny he ever said on stage.

What is certain is that no comedian has proved more culturally significant without moving into TV and films - the means by which the likes of Woody Allen and Adam Sandler achieved wider fame.

The 1974 biopic Lenny, in which Bruce was portrayed by Dustin Hoffman, was nominated for six Academy Awards.

There was a further Oscar nomination for the 1998 documentary Lenny Bruce: Swear to Tell the Truth, narrated by Robert De Niro.

Bruce has inspired or been name-checked in songs by numerous artists including Bob Dylan, John Lennon and Yoko Ono, Nico, REM, Steve Earle, Simon and Garfunkel and Genesis.

He is also one of the celebrities immortalised on the cover of the Beatles's Sgt Pepper's Lonely Hearts Club Band, in the distinguished company of Marilyn Monroe, Karl Marx, Oscar Wilde, Albert Einstein and Gandhi.

In 2003, New York Governor George Pataki granted a pardon to Bruce, following a petition by stars including Robin Williams.

Mr Pataki said the pardon was declaration of New York's commitment to free speech, "one of the greatest American liberties".

Ever the pioneer, Bruce had become the first recipient of a posthumous pardon in New York state history.