He is an enigma from the world's most secretive state, a behind-the-scenes political operative known mostly as a trusted brother-in-law to North Korean strongman Kim Jong Il.
But Jang Song Taek has recently emerged as a decisive player in the drama of who might succeed the ailing 67-year-old Kim in a country that remains defiant in the face of international pressure to dismantle its nuclear arsenal.
Looking weak following a suspected stroke in August, Kim last week publicly anointed Jang as his second in charge, analysts say, naming him to the powerful National Defense Commission.
Pyongyang watchers are divided about the move's significance. Some say Jang could assume power if Kim dies or is incapacitated, while others insist he would merely become the regime's caretaker, ensuring an orderly succession of power to one of Kim's three sons.
"North Korea is a Confucian society wedded to clan and tribe. Kim Jong Il believes only blood clan can continue the dynasty -- and that means one of his three sons," said Jang Sung-min, author of the book "War and Peace: Where Is North Korea Headed After Kim Jong-il?" "But if Kim is incapacitated and does not prepare carefully for his sons, Jang may try to take advantage and seize power."
Jang, 63, has recently accompanied Kim on numerous military and facilities inspections, South Korean officials say. He also reportedly made a secret trip to Europe in March, presumably to visit doctors who treated Kim's suspected stroke.
Analysts are now scrambling to update Jang's diplomatic dossier as a career North Korean technocrat who in 2004 was mysteriously purged from the party power structure, only to return to Pyongyang's political scene 18 months later.
"Jang is a classic political operative, and something of a chameleon, able to switch loyalties on a dime," said Balbina Hwang, a security expert at National Defense University in Washington.
"He may accrue a great deal of power by allying himself with whichever son eventually succeeds to the throne, but he will be behind the scenes."
Gaining intelligence -- including a Jang biography -- from inside reclusive North Korea has often been guesswork, analysts say.
"There is very little credible information, no Pyongyang tabloids to ferret out the juicy details like stories about Princess Diana," said Andrei Lankov, a political scientist at Seoul's Kookmin University who specializes in North Korean history.
"It's all a matter of rumors. North Koreans are very careful about discussing issues of succession and political leadership. Most information comes through intermediaries and the quality is often bad, in many cases pure invention just to sell newspapers."
Yet Lankov believes Jang is clearly on the rise. "They seem to be hedging their bets that Kim won't survive much longer," he said. "He certainly looks unhealthy."
Analysts say that Jang's life and career within North Korea have been marked by luck, family connections and political acumen. Born in 1946, he reportedly studied abroad in Moscow and was educated at Pyongyang's elite Kim Il Sung University.
He began his career in the early 1970s as an economic specialist and has spent the last three decades as a top-level administrator holding various posts in the Workers' Party.
He has overseen the military and secret police and public labor and more recently has pushed to establish economic zones with China.
"He has always been a pure bureaucrat, an economic management specialist," said Lankov. "Today he's running a railway and tomorrow he's torturing political dissenters."
Author Jang Sung-min said his research relied on his experiences as an aide to former South Korean President Kim Dae-jung. In 2000, Kim arranged a historic inter-Korean summit with Kim Jong Il, for which he later won the Nobel Peace Prize.
Jang Song Taek met Kim Jong Il's younger sister, Kyong Hui, while both were students at Kim Il Sung University. "Jang was charming and handsome. He played the accordion, harmonica and guitar. She fell in love with him," the author said.
But the story brought a North Korean twist to the Romeo and Juliet tale. Kim Il Sung disapproved of his daughter's relationship and had Jang moved to another university.
According to a story in the South Korean JoongAng Ilbo newspaper, the fiery Kyong Hui drove her Mercedes two hours to meet with Jang. The two were later married. Both were 26.
Now part of the Kim clan, Jang wielded clout within the regime, especially after Kim Jong Il replaced his late father in 1998. Jang's influence lasted several years before he was suddenly placed under house arrest in 2004.
Jang had allegedly become enemies with Kim Jong Il's second wife, Ko Young Hee, who believed he was scheming for power behind her husband's back.
"She had Kim's ear," author Jang Sung-min said. "She made sure that her rival was taken out of commission until after she died of cancer in 2004." He was released a year later.
Others say Kim was threatened by Jang and banished him to pacify political elites in Pyongyang, adding that Jang's wife played a decisive role in her husband's return to power.
Jang soon repaired his reputation within the party. But the family endured tragedy when the couple's only daughter, Geum Song, committed suicide in Paris in 2006. Analysts say she had wanted to marry a foreigner against her parents' will.
The resilient Jang Song Taek is poised to make his biggest political mark yet on his native North Korea, analysts say. Jang has good relations with all of Kim's three sons and has overseen their educations, experts say. He is believed to back the youngest, 26-year-old Jong Un, as Kim's successor.
"He may think it is the only way to sustain his power," said Cheong Seong-chang, director of the Inter-Korean Relations Studies Program at the Sejong Institute. "If he gives Kim Jong Un a boost as the successor, he would . . . play a role as a guardian."
Despite Jang's slim chances of running the nation, some experts wonder what kind of ruler he would make. "He is a smart man with rationality and reason," said Jang Sung-min. "Who knows, if he took over for Kim, he might take North Korea in a totally different direction."
Ju-min Park of The Times' Seoul Bureau contributed to this report.