Seigo Yamaguchi (1924 – 1996) was born in Fukuoka, Japan.

Between October 1943 and October 1945, he joined the army and actively participated in the Pacific War. He was at that time considering a career in the army, becoming a senior officer by 1949 when he was introduced by a friend to Morihei Ueshiba, the founder of aikido, and became one of his uchideshi (inside student) in 1950.

In 1958-1960, he taught aikido to the military in Burma and after returning to Japan he became one of the senior instructor at the Hombu Dojo and other dojo until his death. From 1977, he travelled extensively in Europe, South America and in the United States to teach aikido at seminars.

Yamaguchi's direct students of note include Yoshinobu Takeda, Seishiro Endo, Masatoshi Yasuno and Christian Tissier.

Yamaguchi Sensei will be remembered for his astounding level of aikido. His had exceptional control and was very relaxed. He had the ability of instantly unbalancing his attackers. There are still many aikidoka today who study the spirit of his movement.