Shiro Saigo was one of the earliest disciples of Judo. Saigo, together with Tsunejiro Tomita, became first in history of judo to be awarded Shodan by the founder of judo Jigoro Kano, who established the kyu-dan ranking system. He was one of the Kōdōkan Shitennō or Four Guardians of the Kodokan along with Yoshitsugu Yamashita, Sakujiro Yokoyama, and Tsunejiro Tomita.

Judo is an unarmed modern Japanese martial art, combat sport, Olympic sport, and the most prominent form of jacket wrestling competed internationally. Judo was created in 1882 by Kanō Jigorō as an eclectic martial art, distinguishing itself from its predecessors due to an emphasis on "randori" instead of "kata" alongside its removal of striking and weapon training elements. Judo rose to prominence for its dominance over established jujutsu schools in tournaments hosted by the Tokyo Metropolitan Police Department, resulting in its adoption as the department's primary martial art. A judo practitioner is called a "judoka" , and the judo uniform is called "judogi" .