SamgukYusa describe that a dragon is god of water such as Poseidon and a sacred beast to symbolize kingship. In some case a dragon is a beast that harms to human beings, in some case it is god of thunder, but in many cases it defends territory of kingdom and protects the Buddhism, to be so in China. In addition a man born between a dragon accedes to the throne. On the other hand, in Japan there is a myth of a large snake, as god of water. It symbolizes the flooding of a river, and to destroy it means to improve the river. Therefore it is exterminated by Hero such as Susanoo. Behind such myth, rich harvest is promised by controlling the river. So the snake is not a symbol of kingship. Why is there such difference? I suppose there are two types of dragon myth. Provisionally I name them as follows. One is “the myth of the maternal dragon “that is handed down among maritime pepole, the other is “the myth of the paternal dragon” that is handed down among agricultural people. The former is a tale that a man having the blood of the dragon becomes a King, the latter is a tale that a man exterminating and controlling the dragon becomes a King. I can find the both types in Japanese myth, but in "SamgukYusa" only the former. Perhaps, what is required to a king in Korea is to protect the country from foreign enemies, more than to control a river. I think the dragon of SamgukYusa was born in such a Korean historical background.