High Quality Content by WIKIPEDIA articles! Yassa (alternatively: Yasa, Yasaq, Jazag, Zasag, Mongolian: Их засаг, Yehe Zasag) was a secret written code of law created by Genghis Khan. It was the principal law under the Mongol Empire even though no copies were made available. Most of this law was supervised by Genghis Khan himself and his stepbrother Shihihutag who was then high judge (in Mongolian: улсын их заргач) of Mongol Empire. Genghis Khan appointed his harshest son Chagatai (later Chagatai Khan) to oversee the execution of it.