Thein Sein has been both a dictator's henchman and a man widely seen as a Nobel Peace Prize contender. He rose to power in a rabidly anti-American military junta, yet spearheaded its efforts to build better relations with the United States.
His past remains opaque, even as he leads Myanmar into a new era of transparency after nearly five decades of dictatorship.
When his quasi-civilian government took power four months after a rigged election in November 2010, Thein Sein was easy to dismiss as a puppet for a still-powerful military lurking behind a new democratic facade. Few predicted what happened next.
Thein Sein launched an ambitious program of political and economic reform that could transform the impoverished nation of 60 million people also known as Burma.
He released political prisoners, scrapped censorship, legalised trades unions and protests, sought peace with ethnic minority insurgents and pushed through legislation on everything from land reform to foreign investment.
Thein Sein's reputation as a corruption-free moderate among hawkish hardliners has earned him widespread praise from world leaders, top economists and Nobel Peace Prize winner and opposition leader Aung San Suu Kyi.
For years the junta's greatest foe, Suu Kyi was released from house arrest a week after the November 2010 election. She met Thein Sein nine months later and, in a critical endorsement, declared him "sincere" about reforming Myanmar.
With his reformist zeal and growing domestic popularity, Thein Sein was widely tipped to win the Nobel Peace Prize in October.
A Western diplomat who has met the bespectacled, soft-spoken president many times described him as "modest, courageous and committed".
"Those who knew him before he became president felt that he was aware of the poverty of his people, had seen the progress made by others in the region and recognized the need for change," he said.
"HIS OWN VISION"
Those comments were echoed by U.N. Secretary-General Ban Ki-moon, who got to know Thein Sein when he was the military regime's prime minister from 2007-2011. He felt Thein Sein had been inspired by the world around him.
"He must have seen and heard the real situation ... the international perception and Myanmar's image," Ban told a group of journalists during his last trip to Myanmar in May.
"As soon as he became president, he has his own visions to make his country better and more prosperous, where human dignity would be respected."
But Thein Sein's reputation still suffers from his role as a loyal servant to former dictator Than Shwe, who during 19 years in power jailed political opponents, gunned down pro-democracy protesters and commanded a military accused of killing, raping and torturing members of ethnic minority groups.
Thein Sein was described last year as "Than Shwe's most malleable puppet" by Irrawaddy, a prominent Myanmar news service long based in neighboring Thailand.
A man of humble rural beginnings and son of a landless farmer and monk, Thein Sein joined the military in his early 20s. But he was always more of a bureaucrat than a soldier, serving as Than Shwe's personal assistant in the 1990s.
He kept his reputation as "Mr. Clean" despite four years as a commander in the lucrative drug-producing Golden Triangle region, where several successors were tarred with allegations of smuggling and abuse of power.
In a 2001 speech to officials in the Golden Triangle, Thein Sein referred to two suspected drug-lords as "real friends", according to Bertil Lintner, the author of seven books on Myanmar.
The two suspects were leaders of the United Wa State Army, described by the U.S. Drug Enforcement Administration as "Southeast Asia's leading heroin and methamphetamine trafficking organization".