Hastrel Jarol was originally a member of the Thieves' Guild that operated out of Imperial City. His family hated him and he never saw them again after he left home. He true name is never known and so he called himself by an imperial name. He was sent on a mission into inner Black Marsh to collect something but was kidnapped and took inside a valley. Where odd looking Argonians imprinted a host into him and he was forever changed.
Hastrel Jarol was eventually joined the Fythun and into a fully grown Kingdom which he personal ruled becoming the founder Ilief of the Fythung.
Elements within the Fythung seek to kill him. Jarol however was ready. He killed the assassins. And went on to become Ilief of the Fythung. During his reign, Jarol built and dwelled in Fort Lorgrim, a mountain fortress that was destroyed during the Polcast War.
Jarol expanded the Fythung's territory, wiping out many Argonians clans. Who believe him to be a god and blow down to worship him and the others. He enslaved them and forced them to work for the Fythung. With the wealth of the Fythung, he continued to lead the Fythung until several years until he was killed by the blade of an assassin. He left his artifacts and the mantle of leadership of the Fythung to his second, Jolpen Imlon.