You know that feeling,” says the American comedian Sarge, “when something happens and you just have to call someone and tell them? And I thought, who can I call?”

The answer was quite as left-field as Sarge’s entire life: chock-full of incident. He made his dramatic phone call to a woman he he’d had no contact with for nearly 40 years — his birth mother. And he spoke to her, for the first and only time, in Las Vegas, making the call from outside the legendary Caesars Palace, where his name was on the marquee, sharing a double bill with singer Paul Anka.

After asking him some questions to make sure he wasn’t a hoaxer, the woman reluctantly agreed she was Sarge’s mother. “Well, I guess you found me”, she said, disclosing the few facts she was prepared to tell him about his birth, before she gave him up for adoption.

He was once one of America’s top comedians. Now he is still in demand for stand-up but is also a high-powered motivational speaker and mentor, an accomplished actor and musician — a man who has re-invented himself over and over again. Because Sarge — real name Stephen Pickman — is an anomaly in America’s melting-pot. He’s both black and Jewish, he’s been a headliner and he’s been a homeless drug addict.

Sarge’s life story began on June 1 1961. His mother, who came from an Orthodox Jewish family in Chicago, somehow had a brief liaison with an African-American musician. Single and pregnant and terrified of what her family would say or do, she fled Chicago for Miami, where she threw herself at the mercy of the head of obstetrics at the city’s Mount Sinai Hospital. She told him she would have the baby but wanted to give it up straight away for adoption.

Enter Grandpa Herman from New York, whose daughter and son-in-law had been desperately trying to have a child and were now ready to adopt. Herman knew someone who could help: his old friend Harry, the head of obstetrics at Miami’s Mount Sinai.

“So Herman called Harry and said, listen, my daughter can’t have kids but she and her husband want to adopt, what can you do?” And Harry said: “As it happens, I got a girl here, lovely Jewish family, wants someone to adopt her baby, she hasn’t had it yet, come down”. He agreed to do all the paperwork, reports Sarge, if only Herman would bring from New York a couple of babka — a sweet brioche which was a speciality of Brooklyn Jewish bakeries.

“The joke was that I was exchanged for two babka”, says Sarge. Herman was present for the baby’s delivery, ready to hand him over to his daughter and son-in-law. But, according to Sarge, “it didn’t dawn on any of them that I was black”. And that, he says, is because a Jewish-black relationship was almost unheard of in 1961.

It’s scarcely credible, this refusal to believe that the little boy was of mixed race, since the swiftest of glances would have told the truth. But Mr and Mrs Pickman, “in denial”, took the child back to Great Neck, Long Island, and raised him as a privileged white Jewish kid.

This was not the gift it might have been. Steve Pickman, as he became, went to a series of smart private schools but did not understand the bullying and racism aimed at him. “I thought it was because they didn’t like me”, he says, “not because I was black.” He would come home every day and ask his parents if he was black. His mother shouted back: “You’re not black! We wouldn’t adopt a black child. You’re from people just like us!” Sarge, relaying this today, says sadly: “Jewish denial”.

But there were two bright spots in the picture: his ability to play music and to tell jokes. The music was identified when he was five or six, after his parents had taken him to see The Sound of Music. Once home he opened the piano and began to play some of the songs — despite never having been taught. The Pickmans immediately took their prodigy to Juilliard Music School for assessment and he began having piano lessons.

The jokes had an even odder origin. Grandpa Herman had a weekly card school in New York where he would play with a group of friends, including people like comedian Henny Youngman. “And Grandpa had already taken me to see Don Rickles at Grossinger’s, in the Catskills. I heard the audience in shambles with laughter; I didn’t know what Rickles was saying because I was only six but I thought, I want to do that.” Herman got his grandson to perform for the card players, jokes that he had taught him. So music and performing was instilled in Sarge very early in life.

Despite the “very low self-esteem; I never liked me” — Steve Pickman seemed set for an impressive career, like all his white Jewish peers. He got a place at prestigious universities, Emory in Atlanta and then Boston; and though he knew he was Jewish culturally and religiously, having been barmitzvah and celebrated Jewish festivals, he had no idea what he was racially.

Instead, he made up stories. “I would tell people I was Cuban or from a lost tribe in Africa, I’d tell them things just to get through — because how could you not know?” He thought that he was probably black but did not know definitively — and, by his own account, did not make many efforts to find out until he was nearly 40.

Though he dropped out of university — where he acquired his nickname, Sarge, for his resemblance to a comic-strip character — he found he could talk himself into any number of high-flying jobs. Aged 24, “a really good people person”, he was a partner in his own model agency in New York — “the only straight guy on the planet that’s a modelling agent in the fashion industry”.

But Sarge, by this time, had developed a thorough-going cocaine habit and his partners bought him out. Undeterred, he got a new job as a sports presenter on TV and, when that didn’t work out, moved on to working for CBS as a presenter. Finally, however, the drugs and drink caught up with him, he was fired by CBS and aged 28, he was homeless. Something then happened which even Sarge, in the telling, can’t really explain.

He had one friend left in New York, Tod, who let Sarge use his apartment while he went on a weekend ski trip. “I robbed him; I stole his jewellery, his watches” — and sold everything for drug money. Tod came back from skiing and realised Sarge had robbed him. He found Sarge on the street in Lower Manhattan, and rather than turn him in, told him: “Let’s get you some help”.

Tod took his friend to a rehab centre in Florida; its first action was to tell him, “Go in to another room and pray for God to remove the obsession [with drugs and alcohol] from your life”. It was December 27 1990 — and it marked the end of Sarge’s addiction. He has been completely clean and sober since.

It was while in rehab that Sarge decided to reinvent himself and use his comic gifts — and he found success over the following decade, working with entertainers such as Donna Summer, Natalie Cole and the Beach Boys. One day, at a Hollywood party, someone suggested he should find out more about his biological parents and he did, signing up to a company which provided him with a family tree. This ultimately led to his only contact with his birth mother.

Then he began to work as a hugely popular comedian on cruise ships, travelling the world for a decade. But in 2005, married for the second time, Sarge had to re-think his career. His wife was heavily pregnant and his parents had moved to Florida. His mother fell and broke her hip, so Sarge cancelled his cruise bookings in order to look after his family.

“And that was the best decision I ever made. I began an on-land career instead”. Now, about 70 per cent of his appearances are to Jewish audiences who rock with laughter at his character assassinations of Jews and blacks alike.

It has to be admitted, however, that Sarge’s stereotypes often leave blacks off worse. Sample: “I’m black and Jewish. I rob stores, but only wholesalers.” Or: “I’m black and Jewish. I hire myself to clean my own house.”

We’ve hardly touched on his other careers as a musician, an actor, and a mentor for substance abuse addicts. But we’ve talked for hours. Sarge laughs. “You gotta tell somebody, right?”