Futabayama Sadaji (双葉山 定次, February 9, 1912 – December 16, 1968) was a Japanese professional sumo wrestler from Oita Prefecture.

Futabayama is particularly remembered for achieving the longest run of consecutive victories in sumo bouts, with 69, a record that still stands today.

However, the percentage of championships won in his makuuchi career still compares favorably to the wrestlers who have surpassed his total in the six tournament a year era.

[2][3] He was one of the first top wrestlers to break away from the tradition of marrying his stablemaster's daughter, instead choosing a young heiress from a rich Kansai family.

He did not take part in the November 1945 tournament and announced his retirement during it, claiming that he objected to the newly enlarged dohyō that the Sumo Association had introduced with hopes to make the sport more pleasing to the occupying forces.

[3] It grew to become one of sumo's largest stables by the 1950s, and Futabayama produced several strong wrestlers including yokozuna Kagamisato and ōzeki Kitabayama and Yutakayama.

In his time as chairman he introduced a number of important reforms, such as giving monthly salaries to wrestlers ranked in the top two divisions, and enforcing a mandatory retirement age of 65 for elders and referees.