Raoh is the eldest of the four adopted children trained by Ryuken, the previous Hokuto Shinken master. The manga and anime gives two different origins thorough the course of the story. In his first origin, Raoh and his biological younger brother Toki, were adopted by Ryuken after their real parents died. A second origin shows that a young Raoh and Toki, along with an infant Kenshiro, were actually refugees who were sent to the "Eastern Land" to be trained in the art of Hokuto Shinken by Ryuken.

Raoh trained under Ryuken along with Toki and Kenshiro, as well as another student named Jagi. In spite of his ambitions to become the greatest martial artist in the world, Raoh lost the rights to the Hokuto Shinken succession to Kenshiro. Refusing to give up the style, Raoh killed his sifu Ryuken in combat and formed his own army, taking the name of Ken-oh, King of Fist. Among his many subordinates includes his adoptive brother Jagi, the Toki impersonator Amiba, Uighur the Warden of Cassandra Dungeon, Juda of Nanto Seiken, and Ryuga of the Star of Sirius, among others. Raoh also begins to ride a large black stallion named Kokuoh-Go (黒王号, Kokuōgō).

(Source: Wikipedia)