Kanō Jigorō
This ranking system was introduced by Kanō Jigorō, the founder of judo, in 1883. However, the current system is not the original one, but based on Kanō's last system introduced between 1926-1931, with some modification shortly after Kanō's death in 1938. The first "dan" grades were awarded to his students Saigō Shirō and Tomita Tsunejirō. Since then it has been widely adopted by modern martial arts.