The Dutch Anton Geesink (1934–2010) started training in judo when he was fourteen, competing in tournaments by seventeen.

Geesink’s first big victory came in 1961 when he beat Sone Koji (1928–1981), the defending champion, at the World Championships in Paris. This victory was pivotal in judo history, as Geesink became the first non-Japanese world champion. This victory is also what caused the elimination of the “open-weight” event at the World Championships. Geesink’s most influential victory came three years later at the 1964 Tokyo Olympics, the first to include judo. He pinned the much smaller Kaminaga Akio (1936–1993) for an ippon. This victory was important because it shattered the myth of Japan’s invincibility in judo and opened the gates for other non-Japanese judoka. The 1964 Olympics were also televised live, which contributed to the international growth of judo.

Some of Geesink’s other notable accomplishments in judo include having his rank of 10th dan recognized by the International Judo Federation and becoming a member of the International Judo Federation Hall of Fame. He also became a member of the International Olympic Committee (IOC) in 1987 and suggested the use of white and blue judogi, which are the suits worn by judoka. Geesink’s time in the committee was marred by his involvement in a vote-buying scandal in 1999 involving thirteen IOC members, but he was allowed to remain in the committee. Geesink also had his own judo club in his hometown, which he taught in.

The 1964 Tokyo Summer Olympics were one of the single most important events in the history of judo.

The 1964 games were the first to be held in Asia, the first to be televised live, and the first to include judo. The hosts claimed gold in the first three events 68kg, 80kg, and 80+kg, but the open category had a surprise in store. The Japanese competitor, Kaminaga Akio, fell to the much larger Dutchman, Anton Geesink. This match was incredibly important for the growth of judo, proving that non-Japanese judoka could compete at the highest level. It led to a surge in the international growth of judo, particularly in Europe.

The 1964 games were a pivotal moment in judo history, leading to it being the first Japanese sport to gain international success and it remains one of the most popular Japanese sports today.

Kanō Jigorō (1860–1938) created judo in 1882 and founded a dojo in the same year which would later be named Kōdōkan. He created judo by combining techniques from jujutsu schools that he was familiar with. He took the striking and strangling techniques from Tenjin Shin'yō and the throwing techniques from the Kito-ryū school.

Kanō is also largely responsible for judo’s accessibility which led to its explosive international growth. Judo was designed to allow a smaller and weaker person to beat a larger, less-skilled person. Women were also accepted at Kōdōkan and spectators were invited to watch tournaments. Another important factor was Kanō’s revision of the ranking system. He created a system of ten ranks (dan) rather than the system of three that was standard in other forms of jujutsu. This change rewarded students more often, encouraging them to continue practicing judo. Kanō was a prominent educator who taught at various educational institutions, founded his own private institution, and also held various positions at the Ministry of Education. Due to this, Kanō was able to spread judo domestically through universities, the Naval Academy, and the Police Bureau. This domestic success encouraged Kanō to introduce judo abroad. Judo found quick success in Europe in the first half of the twentieth century, particularly in Britain, France, and Germany. Judo’s success both domestically and internationally led to its inclusion as an Olympic sport beginning with the 1964 Summer Olympics in Tokyo, Japan.

Tomita Tsunejirō (1865–1937) was the first person to become a live-in student at Kōdōkan. He was only five years younger than Kanō Jigorō and was the student who Kanō spent the most time directly training. Tomita contributed greatly to the early development of Kōdōkan judo by testing jujutsu techniques with Kanō.

Tomita was considered the least skilled and physically gifted of the Kōdōkan “Kings,” but even he had important victories that established Kōdōkan judo as a legitimate form of jujutsu. Namely, his victory over the giant Nakamura Hansuke (1845–1897), known as the “Demon Slayer of the Ryōi shintō-ryū.” He also had his fair share of notable defeats. His worst defeats were at a demonstration of judo to West Point cadets in 1905 and in front of President Theodore Roosevelt (1858–1919) in 1908. Tomita returned to Japan in 1910, where he continued teaching judo as well as American physical education such as boxing and weight lifting. He taught these subjects until his death in 1937, after which he was promoted to 7th dan.

Tomita’s son, Tsuneo, became a famous novelist and managed to reach 5th dan. His most famous work was Sugata Sanshirō, a novel about Saigō Shirō’s life. In 1943, a film adaptation of the book was the directorial debut of the famous Japanese director Kurosawa Akira. Since then, multiple films, TV series, and manga adaptations have been released, turning Saigō into a bigger legend than Kanō.

The details of Saigō Shirō’s (1866–1922) early life are cloudy. He lost his father when he was six, and it is rumored that he was a problem child who constantly got in street fights, a habit that continued into his adult life. Saigō wanted to enter the military academy and become a great general. So, in 1882, he left for Tokyo with his friend. Once he arrived in Tokyo, however, he soon realized it would be impossible to enter the military academy.

After arriving in Tokyo, Saigō originally trained at the Tenjin Shin'yō dojo of Keitaro Inoue. Supposedly, Kanō Jigorō saw him training and was impressed with his talent, so he invited him to train at the Kōdōkan dojo. Saigō became the second live-in student at the dojo. Saigō had some martial arts training prior to entering Kōdōkan, but it is unclear who in Aizu-Wakamatsu taught him. Even Kanō Jigorō himself stated from the beginning that Saigō was hard to handle. Saigō reached 5th dan at age 21, skipping 4th dan in the process. He is said to have been so skilled that after seeing a technique only once he could not only remember it, but improve upon it.

Ultimately, Saigō departed from Kōdōkan sometime after 1886. Kōdōkan claimed that he was expelled, but he claims that he left voluntarily to join the tairiku ronin.

Fukuda Keiko was the longest surviving student of Kanō Jigorō until her death in 2013.

She achieved 5th dan in 1953, which was the limit for women at the time. Following a successful campaign to abolish the limit in 1972, Fukuda Keiko and Noritomi Masako (1913–1982) were awarded 6th dan. In 1994, Fukuda was the first woman to receive the ranking of 8th dan. After being promoted to 9th dan by the United States Judo Federation (USJF) in 2001, another petition was started to grant her the same rank from Kōdōkan. Fukuda waited five years for the petition to be accepted. In 2011, Fukuda received promotion to 10th dan from the USJF, becoming the first women to achieve a rank of 10th dan.

She was a heavy advocate of kata. She was particularly fond of ju-no-kata, which is a stretching exercise that requires no mat or particular uniform and it does not involve throwing so it can be practiced by anyone. She wrote a book on ju-no-kata in 2004 titled Ju-No-Kata: A Kodokan textbook, revised and expanded from Born for the Mat.

Some of her other notable achievements include the creation of the Soko Joshi Judo Club, a women’s judo club in San Francisco that holds classes and kata tournaments. She also established the annual Joshi Judo Camp, a training camp for women from around the world. She was awarded the Order of the Sacred Treasure by the Japanese government, which recognizes long-term public service. Fukuda’s legacy lives on in the annual Fukuda Invitational Kata Championships and the Keiko Fukuda Judo Scholarship.

Yokoyama Sakujirō is famous for being the most physically powerful of the Four Kings of Kōdōkan. He is rumored to have sliced a burglar in half with a sword at only thirteen years old.

Yokoyama trained at the Tenjin Shin'yō ryū, but switched to Kōdōkan in 1886 after losing to the much smaller Saigō Shirō in a challenge match. Yokoyama and Saigō had vastly different styles; Yokoyama was described as a wild boar while Saigō was likened to an expertly trained thoroughbred. Prior to entering Kōdōkan, he was already skilled in the techniques of Tenjin Shin'yō ryū jujutsu, so he was able to reach 2nd dan in just six months at Kōdōkan. Due to his fighting style and incredible raw strength he earned the nickname “Demon.” His nickname is unrelated to “Demon-Slayer” Nakamura Hansuke, but the two did compete in a match that lasted 55 minutes, ending in a tie. Yokoyama, like Saigō, got in many street fights, including stories where Yokoyama won while outnumbered. He was suspended from Kōdōkan on various occasions for his misconduct outside of Kōdōkan.

He wrote one of the first Kōdōkan training manuals in 1915 with Oshima Eisuke, titled Judo Kyohan. It covered judo in the old style, showcasing many pins, locks, chokes, and was notably originally written in English.

Yokoyama hardly taught or trained in his forties, dying prematurely at 49 from esophageal cancer. He was posthumously awarded the first 8th dan in Kōdōkan.

Mifune Kyūzō fell in love with judo in middle school, and it became his sole focus in life. He went to Tokyo under the pretense of further academic studies, but his true goal was to join Kōdōkan. He became a student of “Demon” Yokoyama Sakujirō in 1903.

Although slight in stature, Mifune never allowed his size to inhibit his study of judo. In fact, he claimed that he was “grateful to [his] parents for giving [him] a small body. In order to overcome bigger opponents, [he had] to train twice as hard.” Due to his small size, Mifune worked tirelessly to perfect his technique, which is considered among the best in judo history. His technical expertise is demonstrated in his book, The Canon of Judo (Judo no Shinzui). Mifune also has no recorded losses in formal competitions.

Mifune reached 6th dan in just ten years. 24 years later, Kanō Jigorō promoted him to 9th dan shortly before Kanō’s death. After Kanō’s death, he became the principal instructor at Kōdōkan and is credited for judo’s surge in growth in the postwar period. Mifune was finally promoted to 10th dan in 1945, 42 years after entering Kōdōkan. He never missed a single day of official training in his 62 years at Kōdōkan. He died of throat cancer in 1965 at the age of 81.

Yamashita Yoshitsugu was the son of a minor samurai and was interested in martial arts during his youth. In 1884, this interest led him to the Kōdōkan dojo where he learned judo under Kanō Jigorō. He already had martial arts experience prior to entering Kōdōkan and was well versed in the techniques of the Toshin ryū and the Tenjin Shin'yō-ryū.

Yamashita was an exceptional judo practitioner, achieving 1st dan in just three months and 4th dan within two years. He would later achieve 6th dan in 1898, fourteen years after joining Kōdōkan. He is notable for becoming the first person to reach 10th dan, which was done posthumously in 1935. He had more success in challenge matches than Tomita Tsunejirō, but even so, he never impressed the United States military audiences enough for judo to be considered valuable in their military training. This was largely due to the time it takes to master judo.

Yamashita is also well known as a judo instructor. Among those he taught was former president Theodore Roosevelt. After returning to Japan in 1906, he taught at multiple colleges and at the Police Bureau.