By James Pearson and Stephanie Nebehay

SEOUL/GENEVA (Reuters) - The young Kim Jong Un may be the public face of isolated North Korea, but the man who represents Pyongyang on the international stage is an urbane 75-year-old who lived under an assumed name for decades and survived a vicious purge over a year ago.

Now North Korea's foreign minister and one of the most powerful men in the regime, Ri Su Yong was rumored to have been executed along with his mentor Jang Song Thaek, Kim's uncle, and several of his aides.

But the French-speaking Ri, who acted as Kim's surrogate father when he was at a Swiss school, is touring international capitals again, defending his country's nuclear capability and trying to parry allegations of human rights abuses.

Like Jang, Ri is known as a powerful and close family confidant, open to economic reforms. But Jang fell afoul of the various factions around Kim, possibly because of his rapid rise to power.

Ri returns to Switzerland this week, where he spent two decades as North Korea's envoy to Berne and the United Nations in Geneva and became doyen of the diplomatic corps.

On Tuesday, he will make North Korea's first address to the U.N. Human Rights Council, whose independent inquiry last year accused the regime of committing violations tantamount to crimes against humanity.

"He always struck me as very savvy and sophisticated for a North Korean diplomat. Sophisticated in the sense that he knows the score," said one Geneva-based official who attended frequent diplomatic meetings with Ri.

Unlike other diplomats from North Korea, officially the Democratic People's Republic of Korea, Ri refrained from prefacing his statements with the ideological lectures and ranting against the West that are a hallmark of Pyongyang.

"His formulations were always within acceptable parameters; he was politically correct towards his own country," the official told Reuters. "He was keeping open channels of communication."

Story continues

"He was very pleasant, urbane, not a thug. He was always reputed to be the family's fixer, whatever needed fixing."

Until 2010, he was known as Ri Chol, and was a close aide and friend of Kim Jong Il, Kim Jong Un's father, and by popular account his money-man in Europe. Ri was recalled to Pyongyang in 2010 and in one of the last published photographs of Kim Jong Il before his death in 2011, he is seen standing close to him, with slicked-back hair and thick-rimmed spectacles.

"It's kind of a mystery why he called himself Ri Chol," said Michael Madden, an expert on the Pyongyang leadership. "There are several of these senior guys that are close to the center in Pyongyang and they use different names."

KIDNAP, CLUBS & PARANOIA

A career diplomat, Ri was first dispatched to Switzerland in the early 1980s to establish an official North Korean presence, records held by South Korea's Ministry of Unification show.

But according to a memoir written by Song Hye Rang, the aunt of Kim Jong Un's half-brother, Ri was sent to the Alpine country with another role - to serve in loco parentis to Kim Jong Il's eldest son, Kim Jong Nam, who now lives in effective exile.

It was Kim Jong Un's powerful uncle Jang Song Thaek who recruited Ri to travel to seek out a suitable residence and school in Switzerland, wrote Song, who later defected in Geneva.

But driven by paranoia that South Korean spies might kidnap the dictator's son, Ri spent his early Swiss days in a rented apartment across the road from the school's main gate, which he monitored through a pair of binoculars, according to the memoir.

He later made the family move from a residence he was convinced was under surveillance.

"He placed clubs in various places in the house and instructed us to use them," Song wrote. "He made us constantly feel insecure with stories of being followed and by reminding us that someone was always watching us".

THE 'BUSINESSMAN'

In 2008, Ri was reported to have helped facilitate a multi-million dollar deal between North Korea and Egyptian communications firm Orascom, which runs the country's cellular network. He served as head of the investment committee of North Korea's ruling Workers Party after his return from Switzerland, working with Jang to attract foreign investment.

"There were few cadres in Pyongyang that understood Western thinking so well as Ri Chol and he certainly deserved the nickname of 'Businessman' bestowed on him by his ministry," wrote Felix Abt, a Swiss national who documented his seven years as an executive in Pyongyang in the book 'A Capitalist in North Korea'.

Ri's charm and charisma in dealing with European officials led former Swiss Foreign Minister and President Micheline Calmy-Rey to describe him in a newspaper interview as a "very polite and respected figure in the community of ambassadors" during his long tenure there.

He chaperoned a young Kim Jong Un, who in the 1990s was enrolled in the International School of Berne under the pseudonym Pak Chol and took part in school ski trips but spent much time at home or dining out with Ri.

"We can safely say that Ri Chol is a father figure to Kim Jong Un," said Madden, the expert on the Pyongyang leadership.

(Editing by Tony Munroe and Raju Gopalakrishnan)