Kozo Watanabe, former vice speaker of the House of Representatives, has died at the age of 88, people close to him said Monday.

Watanabe, who was elected 14 times to the Lower House, had retired from politics after deciding not to run in the 2012 Lower House election. The political heavyweight had served as a top adviser to what was then the main opposition party.

A native of Fukushima Prefecture, Watanabe was first elected to the Lower House in 1969 and established himself as a key member of a Liberal Democratic Party faction led by Noboru Takeshita. He also held various posts, including trade minister and home affairs minister.

Together with one-time power-broker Ichiro Ozawa, he left the LDP and joined the New Frontier Party in 1993 after supporting a no-confidence motion against the Cabinet of Prime Minister Kiichi Miyazawa at the time.

Watanabe became the Lower House vice speaker in 1996 and held the post for nearly seven years, a record for the post. He moved to the now-disbanded Democratic Party of Japan in 2005 and became chairman of its Diet Affairs Committee and its supreme adviser.