Masutatsu Ōyama , more commonly known as Mas Oyama, was a South Korean karate master who founded Kyokushin Karate, considered the first and most influential style of full contact karate. Oyama was an ethnic Korean; he was born Choi Yeong-eui and spent most of his life in Japan. He acquired Japanese citizenship in 1968.

Kyokushin (極真) is a style of karate originating in Japan. It is a full-contact style of stand-up fighting and is rooted in a philosophy of self-improvement, discipline, and hard training.