Biryu and Onjo were sons of Jumong, the founder of the northernmost of the Three Kingdoms, Goguryeo. Biryu was recognized as successor of the throne but when Jumong's first wife and Yuri, son of Jumong and his first wife, came and succeeded Jumong, Biryu and Onjo left Goguryeo.
According to the main account given in the Samguk Sagi, Biryu settled in Michuhol, thought to be today's Incheon, South Korea. Onjo settled in Hanam (meaning "south of the river") Wiryeseong in or near today's Seoul. When the Michuhol land proved to be inhospitable, Biryu and his people went to Onjo, demanding that he be the King of Shipje. After Onjo refused, Biryu declared war and attacked Hanam, but failed to conquer it and committed suicide. Later, the two groups merged to become Baekje.
Biryu is also recorded in the Haedong goseungjeon (해동고승전 / 海東高僧傳). A river and a statelet absorbed into Goguryeo shared his name. The 11th king Biryu and the 20th king Biyu of Baekje also apparently took their names from him.