Genghis Khan

Genghis Khan, born Temujin, unified the fractious Mongol and Turkic tribes of the steppe and founded the Mongol Empire, which under him and his successors became the largest contiguous land empire in history. Proclaimed supreme ruler at a tribal assembly, or kurultai, in 1206, he built an army organized on a decimal system with strict discipline and rapid cavalry mobility, and used it to destroy the Western Xia and Jin states in northern China, the Central Asian empire of Khwarazm, and to raid as far west as the Caucasus and southern Russia. His campaigns, especially the destruction of the Khwarazmian cities of Bukhara, Samarkand and Urgench, killed enormous numbers of people, and remain among the most extensively debated events in medieval demographic history. He died in 1227 during a campaign against the Western Xia, having divided his empire's administration among his sons, who under his named successor Ogedei continued the conquests into Russia, Persia, and eventually China itself. Genghis Khan also promulgated the Yassa, a code of law for the unified Mongol nation, and imposed a general religious toleration across his empire that stood in contrast to much of contemporary Eurasia.