Naoto Kan, who has resigned as leader of Japan's main opposition Democratic Party of Japan (DPJ), presented himself as a champion of the people.
Naoto Kan has a grass-roots image
He first came to prominence in 1996, when as health minister he came clean about a tainted blood scandal involving his ministry.
He forced bureaucrats to release documents which showed the government had failed to prevent the use of HIV-infected blood products for transfusions.
The scandal provoked a public outcry, and his handling of it propelled him to the opinion polls' favourite for Japan's next prime minister, ahead of current leader Junichiro Koizumi.
But now his spell as health minister has proved his downfall, after he admitted that he failed to make payments into the state pension scheme for 10 months while he was in the job.
Although his failure to pay was an apparent oversight, and the amounts involved were relatively small, Mr Kan said he was resigning to avoid further damaging the DPJ.
Internal divisions within Mr Kan's party, and a sex scandal in 1998, in which he was linked with a television newscaster, chipped away at his support base. Known as "Ira-Kan" or "Fretful-Kan", he is reputed to have a short temper.
But in 2003 elections, Mr Kan and the DPJ made a strong comeback, establishming themselves as a credible opposition to Mr Koizumi's Liberal Democratic Party (LDP), and prompting talk of Japan becoming a two-party political system.
Before his resignation, Mr Kan presented the DPJ as the only party that could truly reform Japan's economy and administration. He said the vested interests of the LDP members meant it would never be able to do so.
Mr Kan was born in 1946 in Yamaguchi Prefecture in western Japan - the second child and only son of a local businessman.
He graduated in physics in 1970 from the Tokyo Institute of Technology, and went on to set up his own patent office in 1974.
It took persistence for Mr Kan to break into politics. Actively involved in various civic movements, he lost three elections before winning his first seat in the lower house in 1980 for the now-defunct United Social Democratic Party (USDP) with a "civil guerrilla" grass roots environmental campaign.
He is married with two sons, and lives in western Tokyo.
He lists the ancient and notoriously difficult Japanese game of Go among his hobbies, and is said to enjoy shochu, a strong drink traditionally preferred by Japan's working class men.