He came to power by uniting many of the nomadic tribes of Northeast Asia. After founding the Mongol Empire and being proclaimed "Genghis Khan", he started the Mongol invasions that resulted in the conquest of most of Eurasia. These included raids or invasions of the Qara Khitai, Caucasus, Khwarezmid Empire, Western Xia and Jin dynasties. These campaigns were often accompanied by wholesale massacres of the civilian populations – especially in the Khwarezmian and Xia controlled lands. By the end of his life, the Mongol Empire occupied a substantial portion of Central Asia and China. 

Before Genghis Khan died, he assigned Ögedei Khan as his successor and split his empire into khanates among his sons and grandsons. He died in 1227 after defeating the Western Xia. He was buried in an unmarked grave somewhere in Mongolia at an unknown location. His descendants extended the Mongol Empire across most of Eurasia by conquering or creating vassal states out of all of modern-day China, Korea, the Caucasus, Central Asia, and substantial portions of modern Eastern Europe, Russia, and Southwest Asia. Many of these invasions repeated the earlier large-scale slaughters of local populations. As a result, Genghis Khan and his empire have a fearsome reputation in local histories.
Who founded the Mongol Empire?
Genghis Khan