Ryūō (リュウオウ) is a son of the Hokuto Sōke clan who lived in the Land of Asura sometime around the 2nd or 3rd century. Born to a woman named Ōka on the same day as Shuken (the son of Shume, Oka's sister), high priests forbade the existence of two male heirs to the clan, so they left Ryuo and Shuken exposed to a pack of starving wolves so that the surviving child would be handed the task of developing the clan's ultimate martial art. Due to Shume's, interference in the ritual, Ryuo was the original chosen successor, but lost the title after Oka offered herself as a sacrifice so that Shuken would grow up to be the successor (with Ryuo in a subordinate role). Growing up as a lost man due to the lack of motherly love, Ryuo and all of his descendants (Kaioh, Raoh, and Toki) were fated to seek that lost love in their lives.
In the anime series, it is established that Ryuo left the clan after growing up and became the founder of Hokuto Ryū Ken.