Yamaguchi-gumi (Japanese: 山口組) has been known as Japan's largest boryokudan (analogous to a western Mafia family). Estimates put the number of active members at 20,000, with another 15,000 people having strong associations. It is, by far, the largest of the yakuza groups, and its membership encompasses roughly a third of all yakuza. The Yamaguchi-gumi has its headquarters in Kobe, Japan, but it operates all across Japan, and also has overseas operations in Asia and the United States.

Leadership

• 1st (1915-1925) Kumicho: Yamaguchi Harukichi
• 2nd (1925-1942) Kumicho: Yamaguchi Noboru - son of Yamaguchi Harukichi
• 3rd (1946-1981) Kumicho: Taoka Kazuo

After the death of Taoka, the heir apparent was was serving sentence in prison. He, however, dies shortly afterwards of liver failure. Kumiko Taoka, Kazuo Taoka's wife, stepped forward to fill the leadership void until a new kumicho could be selected.

Finally, in '84, the elders chose Takenaka Masahisa to be the 4th kumicho of Yamaguchi-gumi. One of the other contenders, Hiroshi Yamamoto, broke away from Yamaguchi-gumi with more than 10,000 of its members to form Ichiwa-kai . A bitter rivalry existed between the two groups, which was exacerbated by Ichiwa-kai's 1985 assassination of Masahisa.

• 4th (1984-1985) Kumicho: Takenaka Masahisa
• 5th (1989-) Kumicho: Watanabe Yoshinori