Japan's Prime Minister Naoto Kan, who survived a bruising challenge for the party leadership Tuesday, is a one-time social activist with the image of the humble "son of a salaryman".
Having defeated veteran powerbroker Ichiro Ozawa, he must now unite and lead their centre-left Democratic Party of Japan (DPJ) as it enters its second year in power, 12 months after it ousted the long-ruling conservatives.
The party ballot victory is a much-needed boost for Kan, an unelected premier who took over Japan's top government job in June after the DPJ's first premier Yukio Hatoyama stepped down with rock-bottom approval ratings.
Kan was quickly criticised for squandering his political honeymoon, marked by the slogan "Yes, we Kan", when he presided over an upper house election rout in July that was widely blamed on his pre-election talk of raising taxes.
His DPJ election win three months later comes close to a popular vindication, since Kan won a large majority among the party's 340,000 rank-and-file members and led among ordinary voters according to media polls.
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In his fight against Ozawa, Kan stressed his desire for "clean politics" and an end to old-style backroom deal-making, which many voters associate with Ozawa, who is the subject of an inquest over campaign finance irregularities.
Unlike Ozawa and many other Japanese lawmakers, Kan was not born into a privileged political dynasty but gained his first parliamentary seat through tough campaigning, winning only on his fourth try in 1980.
"I'm the son of an ordinary salaryman," he said in June, aligning himself with the country's army of white-collar workers.
"Young people raised in ordinary families, with ambition and effort, can make it big in the world of politics. Isn't that what real democracy is all about?"
Kan was born in Yamaguchi prefecture, the son of a factory manager.
A graduate of applied sciences from the prestigious Tokyo Institute of Technology, he once invented a points calculator for the popular game mahjong but failed to pitch his prototype to Nintendo and other makers.
He became a leading civic activist in the 1970s, pushing for pacifist and environmental causes as the protege of a well-known feminist campaigner, before entering mainstream politics with a small party.
Kan gained popularity during a stint as health minister in the mid-1990s, when he exposed government culpability in a scandal over HIV-tainted blood products that infected more than 1,000 people.
When the DPJ took power last year, ending more than half a century of conservative rule, Kan became deputy premier. He took over as finance minister in January despite admitting he was no economics expert.
Kan had to step down during a previous stint as DPJ leader, in 2004, after admitting he had neglected to pay full state pension contributions, having earlier attacked ruling party lawmakers for failing to do so.
In a display of atonement, Kan shaved his head, donned a Buddhist robe and went on a pilgrimage to temples on the island of Shikoku.
He faced another scandal after a gossip magazine revealed he had spent a night in a hotel room with a television presenter. Kan managed to save both his political career and his marriage to wife Nobuko, with whom he has two sons.
Happy to break with the stereotype of the demure wife, sharp-tongued Nobuko relishes the role of Kan's toughest critic and famously spars with him over everything from household chores to tax reform.
In a book she published earlier this year, she quipped that she had only taken a set of summer clothes to the prime minister's residence -- a reference to Japan's notorious "revolving-door" procession of short-lived PMs.
At least for now, Kan has won that battle too.
