In the flesh, he is a force. Dressed head to toe in black, with an Indonesian bandana around his forehead, Ndesandjo is tall and personable, and speaks with a warm American accent. He's much more likeable than his self-deprecating new autobiography, , suggests.

and Barack couldn't have unfolded more differently. While Barack's childhood was a happy Honolulu existence, Mark spent his formative years in a newly independent Kenya, living under the reign of terror of an alcoholic and abusive father, until his white, American mother finally found the courage to flee.

Despite his Kenyan upbringing, Ndesandjo never felt accepted by black Africa; but as the son of a Luo tribesman, he also felt incongruous in the expatriate community to which his mother belonged.

With his first autobiography, which was released last month, Mark has emerged from relative anonymity to tell his story and set the record straight about the president's "mysterious Kenyan roots".

"I wanted to tell my story myself without other people telling it for me," he says.

Ndesandjo, 48, lives in Futian, Shenzhen, with his wife, Liu Xuehua, a Henan province native and his partner of a decade. The pair met in a tea shop when Ndesandjo was an impoverished English teacher. He had emigrated to China in 2003 from Orlando, Florida. Having lost a well-paid job in the telecommunications industry in the post-9/11 economic slump, he wrote to the director of a mainland teaching project he'd read about in a magazine, asking for a job.

"He said, 'You're obviously too qualified.' But I really wanted to explore China."

Ndesandjo expected to stay for three months. Twelve years later, he is fluent in Putonghua, proficient in calligraphy and has no plans to leave the country. Long-standing rumours tell of him running a barbecue restaurant in Shenzhen, but he laughs them off.

"I'm a vegetarian," he says.

What he does run is a foundation that helps children in need, while also teaching piano to orphans, raising awareness of domestic violence and heading up two consulting companies that assist American investors entering the Chinese and Kenyan markets, and those looking to go in the other direction, one registered on the mainland, the other in Hong Kong.

met Obama was in 1988. It was a sunny weekend in Nairobi, and Ndesandjo was on his bed reading Fawn M. Brodie's , about the explorer Richard Burton.

"My mother came to the doorway and was trembling. She said, 'Your brother from America is here. In the living room. He wants to meet you.'"

In Obama's 1995 autobiography, , he claims Ndesandjo's mother, Ruth Baker, sent a car to pick him up and that the family had arranged lunch.

"It was never like that," Ndesandjo says, shaking his head. "He and my half-sister, Auma, walked in that afternoon out of the blue. It was a year after my younger brother, Bobby [David Opiyo], had died in a motorcycle accident. I thought, 'What are they doing here?'"

Obama, Ndesandjo remembers, sat on the couch in very simple clothes, appearing as a regular Kenyan, with gangly legs and arms, and huge hands.

"My stepfather [Simon Ndesandjo] was very impressed by him," he says.

The family leafed through photo albums but the meeting was stilted, and the two half-brothers agreed to meet again a few days later.

"He looked so similar to me, we both loved America and were going to Ivy League schools," he says.

Having left Kenya aged 17, armed with a scholarship, Ndesandjo had just completed a degree in maths and physics at Brown University, in Rhode Island. He was on a break in Nairobi before returning to the US, to enrol at Stanford University.

"Until then, I'd assumed I was the cleverest in the family," he says.

But the long-lost siblings failed to connect.

"Barack felt I was too Western, and I thought he was trying too hard to be African," Ndesandjo remembers. "He wanted to know a lot about my father [who had passed away in 1982], and he was very direct with his questions. I felt like he was opening up old wounds. A lot like a lawyer, he was trying to research our emotional history.

"He kept asking, 'Well, what do you think of him?' I had shut all these things out, but he was relentless. It was a shock to him when I said, 'Our father was a drunk and he beat women.' Barack flinched. He wasn't aware of that.

"I think that has coloured our relationship to this day. In fact, I know it has."

Barack Obama Snr had skin as dark as ebony, teeth that shone like pearls and, in his younger years - like his Hawaiian son - had the hallmarks of brilliance. Born in 1936 in the sun-basked Nyanza province of western Kenya, Obama Snr attended the prestigious Maseno School, where his teachers described him as an "exceptionally bright student".

However, Obama Snr didn't graduate from high school, the record shows, because of a "behaviour infraction". Consequently, in 1959, his request for a grant to study abroad was rejected. Had it not been for Elizabeth Mooney Kirk - a forty-something American who Obama Snr allegedly seduced - agreeing to bankroll him, neither Barack Obama nor Ndesandjo would be here today.

It was the Swinging Sixties in Boston when Obama Snr met Baker at a party. She was a Jewish girl from Massachusetts, born to first-generation Russian and Lithuanian immigrants, he was a Harvard graduate who was "a touchy, sarcastic but incredibly charming intellectual", according to Ndesandjo.

In August 1964, after two months of dating, Obama Snr proposed. Smitten and seeking adventure, Baker relocated to Nairobi, where her new partner should have been on a fast-track government career - prospects that were squandered in bars.

"At this point," Ndesandjo says, "my mother didn't know about Barack and his mother, Ann Dunham," who had married the African student in 1961 and divorced him three years later. Obama Snr saved that surprise for when he and Baker were in Kenya, where a picture of Barack II eventually sat on the mantelpiece of the couple's first home.

Life in the Obama household was hell. Baker says in her memoir that, from the start, Obama Snr "was drinking heavily, staying out to all hours and hitting me". Within a year, she had fled back to the US.

One night, after Obama Snr had persuaded her to return, he came home drunk and held a knife to his wife's throat. Shortly after, Baker had her seven-year marriage annulled. Ndesandjo was seven years old. Even today, thousands of miles away in Shenzhen, when Ndesandjo remembers his father's violence, tears slide down his cheeks.

Ndesandjo can't remember being told about his father's death.

"Perhaps I blocked it out," he says. "When Barack came to Kenya, I felt he admired our father because Obama Snr had been proud to be a black African; a person who wouldn't let anyone get in the way of Kenyan independence and the flow of free ideas. But I wanted to be as far away from him as possible."

After that first meeting between the half-brothers, Ndesandjo returned to the US, where he studied for a master's degree in physics at Stanford University, before preparing to take a PhD. Then, in a moment of weakness, he cheated. In his autobiography he describes the giddy moment he slipped into his professor's office to read the exam paper: "I had the keys to the kingdom."

He was caught and then suspended by the department chair, Steven Chu, who, in a twist of fate, would later work for the Barack Obama administration as secretary of energy. Ndesandjo describes feeling suicidal as he left Stanford mired in disgrace.

Two decades in the corporate world followed. During this period, Ndesandjo dropped the Obama name and never returned to Africa; didn't speak to his half-siblings - Malik and Auma - by his father's first wife, Kezia; and didn't return to see his mother. He did, however, dip in and out of contact with Barack.

Once, the pair went for lunch in San Francisco at Tommy's Joynt, a haunt for hippies and left-wing progressives. Obama again had questions about Kenya.

"I felt he was clarifying facts from years before."

A few months later, aged 33, Obama published - an autobiography he'd never prepared his family for. Ndesandjo uses to right the many wrongs he sees in his half-brother's opus.

"I think he took artistic licence with the book. He created composites of characters, and he didn't like my mother. There was also a playing up of our wealth in Kenya. We could never have afforded to send a car for him."

In 2004, the year after Ndesandjo had moved to Shenzhen, a friend drove him to the American Chamber of Commerce in Guangzhou, to watch the new Illinois state senator, Barack Obama, give the keynote address at the Democratic National Convention in Boston, which would make the politician an overnight star. As Ndesandjo and a gaggle of other Americans watched the senator speak live, before a rapturous audience waving Obama placards, Barack told the world, "We are our brother's keeper."

"At that point, no one knew of my relation to him, except the friend who had driven me over," Ndesandjo recalls. "But word gets around, and someone asked, 'Are you his brother?' I said, 'Yes'. Suddenly, I felt very proud of him."

A few days later, a friend called up. "It's great that he got that speech," the friend said. "But he'll never have a chance at being president."

Ndesandjo doesn't remember where he was when Obama made history by announcing his candidacy for president, in 2007. But he quickly renewed contact, sending his half-brother e-mails with quotes from Sun Tzu's as the campaign thundered forward.

"Feint to the east and attack the west," he e-mailed when his challenger for the Democratic Party presidential nomination, Hillary Clinton, focused on capturing big states, "Revive in a new guise," when Obama decided to directly attack Clinton in Ohio and Texas.

Barack's campaign started to heal the Obama clan, which Ndesandjo likens to "herding cats, all moving in their own direction". Ndesandjo flew to the US to meet a half-brother, Joseph, from his mother's second marriage, to support Barack at his 2008 Democratic Party presidential debate against Clinton in Austin, Texas.

When Barack was elected, the entire Obama family was flown out to the White House for the inauguration; not an eyelid was batted when Malik came attired in a Muslim fez. As they toured the Oval Office, Barack promised he would one day meet Ndesandjo's wife in China.

"But he declined an invitation to our Shenzhen home for dinner," Ndesandjo remembers, "Barack said, 'They won't let me.'"

They, of course, would have been the White House security department. How much influence did Washington have on his own movements at that point?

"I've never gotten the impression they've tried to control what I do," says Ndesandjo. But his paranoia had compelled him to flag certain "failures" that he felt the Republicans might have been able to use as weapons in the fight for the presidency. First, his suspension from Stanford, and second, a trail of bad debt he had left in the US. Obama replied with a brief e-mail: "Mark, do not worry - your life is your own and will not affect my election."

In 2008, Ndesandjo and Liu married in a low-key ceremony. Their union is one of harmonious compromise; they speak Putonghua during the week, English on the weekends and eat separate meals - Ndesandjo is not partial to "squidgy" Chinese cuisine. He says their "otherness" is what fascinates both parties, and cites her as his rock.

It was Liu who, in 2009, encouraged Ndesandjo to pursue a lifelong ambition he knew would have long-standing familial repercussions. That year, he published , a fictionalised account of his past, but one accurate enough for the world's press to realise Ndesandjo had outed Obama Snr - the man Barack had lauded as an example of the American dream in that famous 2004 keynote speech - as a wife beater and a drunk.

The opening scene of is of Ndesandjo's long-promised meeting with Obama in Beijing, shortly after the novel was published. The half-brothers talk for five minutes and Ndesandjo describes the president as smelling vaguely of cigarette smoke and being emotionally closed. Later that day, Obama told a CNN journalist: "I don't know [Ndesandjo] very well. I met him for the first time only two years ago."

Those words stung.

"I sometimes feel we - the Obama family - have been used. Since being elected, Barack has been trying to distance himself from his relations in Kenya, and he's overly sensitive to the African dimension of his past. That's not right."

The two haven't seen each other since, but remain in e-mail contact.

"A few months ago, I said, 'Barack, you have to try and reach out more. One word to the family in Kenya - a happy birthday to Granny Sarah, who is 93 - would mean the world.' He got quite upset about that."

Still, Ndesandjo recognises the tremendous opportunities his half-brother's fame has afforded him, and is convinced Obama has been a "great president who is fundamentally trying to make good in the world".

The Obama family, Ndesandjo says, spanning Islam, Judaism, Kenya, the US, China, Indonesia - on Barack's side - and Mexico - through Joseph's wife, Dora - is a tale of what it is to be a modern, multicultural American. As his maternal Grandma Ida says in : "One day, Mark, we will all be brown."

Ndesandjo says he has made peace with Obama Snr, Barack's achievements finally having made him proud of the family name. In 2011, after 20 years away, he returned to Kogela, the family village in Kenya.

"It's funny," he says. "In , Barack says sons often spend their lives trying to achieve their father's dreams or correct their errors. That polarity defines my relationship with Barack. I've been trying to correct the issues I experienced with my father my whole life. Barack, on the other hand, has been achieving my father's goals and dreams."