Lenny Bruce died 50 years ago this week, sitting on the lavatory with a syringe in his arm. His electric typewriter was still purring: "Conspiracy to interfere with the 4th Amendment cons…" He had stopped mid-word in one of the desperate legal arguments that were obsessing him. He was 40 years old.

The official cause of death was "acute morphine poisoning caused by an accidental overdose." But his friend, the record producer Phil Spector said he died of "an overdose of police."

Lenny Bruce was buried in Mission Hills, California. His headstone bears a Magen David and the words: "Lenny 'Bruce' Schneider, Beloved Father - Devoted Son. Peace At Last." In his case, the cliché carried an unusual burden of truth.

He was a comedian who talked about sex in a way nobody on a public stage had done before. No euphemism or innuendo - lots of four-letter and 12-letter words. He attacked injustice and hypocrisy full blast and lacerated the Catholic church: "Why are there Puerto Ricans starving in New York while Cardinal Spellman was wandering round wearing a $8000 ring?"

You didn't ask questions like that, certainly not on stage. Bruce was good-looking, sharp, very Jewish and incredibly hip. His performance was a flowing improvisation, more like a jazz solo than a traditional comedy act. His treatment by the police was horribly similar to that meted out to black musicians.

Beatniks like Alan Ginsberg, hairy and homosexual, were appalling enough to mainstream America but Ginsberg was only a poet. The new comedians were far more disturbing. Time magazine called them "sickniks", singling out Mort Sahl, the sharpest political satirist, and Tom Lehrer, the Harvard mathematician who wrote funny, disrespectful songs.

All these Jews! But Lenny Bruce was the worst. There seemed no limits to what he would say.

Later, when he had been brought to his knees by harassment and arrests and was facing his final trial in New York, his high-profile supporters in court included Woody Allen, Bob Dylan and Norman Mailer. To all three of them, he was a hero.

Discharged from the navy in 1945 after displeasing his commanding officer by performing a drag act, he embarked on his comedy career.

By 1951, he was in an act that involved his mother Sally Marr, who had a low-key show-business career and, his wife Honey Harlow, who had been a stripper. Through the decade he developed his idiom - "blue, sick" - and he gathered a following.

In 1959, he made it on to Steve Allen's networked chat show. His script was carefully typed out and fiercely adhered to. He had a big following by then but Allen's support was enormously valuable, a great step up from the clubs he had been working.

Two years later, Bruce played Carnegie Hall on a blizzardy night and gave a performance that became famous. In the words of his biographer Albert Goldman: "he finally reached a point of clairvoyance where he was no longer a performer but rather a medium transmitting messages that came from him from out there - from recall, fantasy, prophecy. His tongue would outrun his mind and he would be saying things that surprised, delighted him, cracked him up."

It was staggering and it had tremendous impact on later comedians, most notably Robin Williams. The whole modern idiom known as stand-up proceeds down a path opened by Bruce.

On his album, What I Was Arrested For, there are a couple of routines with characters and conversations that are dead (pre)ringers for Eddie Izzard, in particular Izzard's Darth Vader at the Death Star Canteen, more salubrious, equally funny and in conduct and vocal timbre almost identical. And Izzard has played Bruce in a play in London.

The late Joan Rivers, speaking in 2014, told a story of how Bruce saw her show bomb.

"And he sent me a note, 'you're right, they're wrong.' I held it in my bra!" Years later, she learned that Bruce had encouraged many young comedians with the same words.

Rivers cited Bruce as a key influence, because he: "told the truth, and that's what I try to do."

Telling the truth got Bruce into trouble. The rooms he played were increasingly full of policemen just waiting to pounce. He made one trip to London in 1962 to play at Peter Cook's Establishment club; the following year, he was denied entry to Britain as an "undesirable alien".

Bruce's career divides into three sections. From 1957 to '61, he was a funny, hip, sexy comic; from late 1961 to '63, he was sinking deeper into drugs; then, from 1964, when he had been arrested many times, he was bloated and sick and his act was unfunnily preoccupied with his own horrible predicament.

In a country constitutionally committed to free speech, how can you be arrested for obscenity?

In New York in 1964, the prosecution had to prove that he had provoked "lustful and lecherous thoughts". After a wait of 99 days and with Bruce begging to bring new evidence, the judge sentenced him to four months in the workhouse. While he was free, pending his appeal, he died.

One of his prosecutors said: "I feel terrible about Bruce. We drove him into poverty and then bankruptcy, then we murdered him."

A eulogy in Playboy magazine ended: "One last four-letter word for Lenny: Dead. At forty. That's obscene."

In 2003, a campaign supported by Robin Williams petitioned New York's governor, who granted Bruce the first posthumous pardon in the state's history.

How would Bruce's comedy be received now? Just look at Chris Rock, who has stopped playing American colleges, saying: "You can't even be offensive on your way to being inoffensive."

If Bruce were around today, no doubt he'd still be telling his offensive, obscene, profanity-peppered truth.