Gunji Koizumi

, known affectionately by colleagues as G.K., was a Japanese master of judo who introduced this martial art to the United Kingdom, and came to be known as the 'Father of British Judo.' He was the founder of the Budokwai, a pioneering Japanese martial arts society in England. Koizumi helped establish the British Judo Association, and founded the European Judo Union. He was the younger son of a tenant farmer, Shukichi Koizumi, and his wife, Katsu. Koizumi had an elder brother, Chiyokichi, and a younger sister, Iku. During this period, Koizumi also taught jujitsu at the London Polytechnic and for the Royal Naval Volunteer Reserve. After several months, he set off for New York, arriving in May 1907. In 1932, he was promoted to 4th dan in judo.

Through World War II, judo training continued at the Budokwai, but at great financial cost to Koizumi. He served as the association's inaugural President. who later married Percy Sekine, one of Koizumi's judo students.

Later life

On 19 September 1954, the Budokwai moved to new, larger premises; shortly after this, Koizumi returned to Japan for the first time in 50 years. and My study of Judo: The principles and the technical fundamentals (1960). He continued teaching judo throughout the early 1960s.

The night before Koizumi died, Charles Palmer (one of Koizumi's students) sensed that something was amiss—Black Belt magazine correspondent Kei Tsumura relates that "instead of his [Koizumi's] usual smiling 'good-night', he shook his [Palmer's] hand and said 'good-bye'" (p. 50).

Koizumi's death shocked the worldwide judo community, and caused much controversy.