Sosai Mas Oyama (Yong-I-Choi) was born on 27th July 1923 in Gimje, Imperial Japan (now South Korea). At an early age, he lived on his sister's farm in Manchuria, Northeast of China, and attended Yongree Primary School. He studied Southern Chinese form of Kenpo, also known as Eighteen Hands. When he was 12 he decided to return to Korea but kept his best interest in martial arts.

In 1938, Oyama went to Japan following his brother who enrolled in the Yamanashi Aviation School Imperial Japanese Army aviation school. It was where he earned the name of Oyama Masutatsu, which is a transliteration of 'Baedal'. 'Baedal' was an ancient Korean kingdom known in Japan during Oyama's time as "Ancient Joseon".

In 1946, Oyama enrolled in Waseda University School of Education to study sports science. Wanting the best in instruction, he contacted the Shotokan dojo (Karate school) operated by Gigo Funakoshi, the second son of karate master and Shotokan founder Gichin Funakoshi. He became a student, and began his lifelong career in Karate.

In 1947, Mas Oyama won the karate section of the first Japanese National Martial Arts Championships. Wanting to devote his life to karate, he spent the next few years from human society, training in the mountains 12 hours per day, every day. His training methods included standing under icy waterfalls, breaking river stones with bare hands, striking tree trunks to strengthen his hands and weight training with large boulders. He also developed his jumping ability by leaping over flax plants hundreds of times each day.

In 1950, Sosai began testing (and demostrating) his power by fighting bulls, that were destined for slaughter. In all, he fought 52 bulls, three of which he killed instantly, and 49 had their horns taken off with knife hand blows. In 1952, he went to the United States and tested himself against professional boxers, wrestlers and anyone else who would accept the challenge. In all, he fought 270 challengers, defeating every one of them. It was where he earned the nickname of The Godhand.

In 1953, Sosai opened his first dojo, which was an open air dojo in the burned out ruins in Mejiro, Tokyo. His training methods were very hard and involved pretty much full contact fighting. Due to the intensity and severity of the training, the drop out rates were very high, but eventually he had over 700 students and in 1964 he moved his dojo to Tokyo's Ikebukuro district, which would serve as the Kyokushin world headquarters.

In 1969, Sosai launched the first All-Japan Full Contact Karate Open Championships which took Japan by storm and Terutomo Yamazaki became the first champion. As the 1970s approached, he launched the first World Full Contact Karate Open Tournament in Tokyo, and in 1977, he attended the first Australian Full-Contact Championships held in Sydney.

Later in life, Oyama suffered from osteoarthritis. Despite his illness, he never gave up training. He held demonstrations of his karate, which included breaking objects. He wrote over 80 books in Japanese and some were translated into other languages. Sadly he passed away of lung cancer on April 26, 1994. He was a non smoker.

Since the death of Sosai, all Kyokushin organizations still maintain the standards set by Mas Oyama for the sake of many generations to come. This is why it's the responsibility for all of those who chosen to follow Sosai, to train hard and forge and indomitable spirit so that the tradition of strength in Kyokushin Karate may be recognised by all for many years.