Ligdan Khan
During the early period of the Northern Yuan dynasty (1368-ca.1636), shamanism once again became the sole dominant religion in Mongolia, but the last sixty years before the death of the last khan Ligdan Khan (1588-1643) were marked by intensive penetration of Tibetan Buddhism into Mongolian society. In 1578, Sonam Gyatso was invited to Mongolia and converted Altan Khan to Buddhism along with his tribe (the first Mongol tribe to be so converted). Altan Khan conferred the title "Dalai" on him, "Dalai" being the Mongolian translation of his Tibetan name "Gyatso", which means "sea" or "ocean". This is the origin of the title Dalai Lama. The Ming assisted Altan Khan (1507–1582), King of the Tümed Mongols, when he requested aid in propagating Vajrayana Buddhism. Within 50 years nearly all the Mongols had become Buddhists, including tens of thousands of monks, almost all followers of the Gelug school and loyal to the Dalai Lama. Since then Tibetan Buddhism has played a very important role among the Mongols.