TOKYO (Reuters) - Japanese prosecutors were set to question the ruling Democratic Party’s powerful No.2 official on Saturday over a funding scandal that threatens the party’s chances of winning a key mid-year election. Prosecutors last week arrested three current and former aides to party Secretary-General Ichiro Ozawa over the affair, adding to the woes of Prime Minister Yukio Hatoyama’s four-month-old government.

Ozawa has been a pivotal figure in Japanese politics for decades, first as a wunderkind in the long-dominant Liberal Democratic Party (LDP) and then as a reformist rebel trying to topple his former allies from power.

Following are some facts about Ozawa:

* Born in 1942, Ozawa was first elected to parliament as a member of the conservative LDP at the age of 27 and rose rapidly through the ranks as a protege of party kingpins including Kakuei Tanaka, the father of Japan’s modern pork-barrel politics. Promoted to LDP secretary-general at the age of 47, unusually young for Japan, he was once considered a candidate for prime minister.

* In 1993, Ozawa left the LDP with about 40 other lawmakers, setting off a chain reaction that ended the party’s rule after four decades and briefly replaced it with a reform-minded coalition.

That same year, Ozawa outlined his policies in a book, ‘’A Blueprint for a New Japan’’, calling for a bolder security role, reforms to reduce bureaucratic control and underscoring the need for a viable rival party to the LDP.

* After the LDP returned to power in 1994, Ozawa formed a series of new parties, one of which briefly rejoined an LDP-led ruling bloc.