垂仁天皇
The "Nihon Shoki", published in 720, dates the first sumo match between mortals to the year 23 BC, when a man named Nomi no Sukune fought against Taima no Kuehaya at the request of Emperor Suinin and eventually killed him, making him the mythological ancestor of sumo. According to the "Nihon Shoki", Nomi broke a rib of Taima with one kick, and killed him with a kick to the back as well. Until the Japanese Middle Ages, this unregulated form of wrestling was often fought to the death of one of the fighters. The first historically-attested sumo fights were held in 642 at the court of Empress Kōgyoku to entertain a Korean legation. In the centuries that followed, the popularity of sumo within the court increased its ceremonial and religious significance. Regular events at the Emperor's court, the "sumai no sechie", and the establishment of the first set of rules for sumo fall into the cultural heyday of the Heian period.