The correct answer is A, as Genghis Khan united the Mongol tribes; and was known as the "ruler of men".
Genghis Khan (1162-1227) was a Mongolian warrior and conqueror who unified the nomadic tribes of this ethnic group of northern Asia, founding the first Mongol Empire, the largest contiguous empire in history. Under his leadership as the Great Khan, the Mongols began a wave of conquests that extended their dominion to a vast territory, from Eastern Europe to the Pacific Ocean, and from Siberia to Mesopotamia, India and Indochina. In the first phase of this expansion, the Mongol hordes conquered important kingdoms of Asia, such as the Jin Empire of northern China (1211-1216), the Tanguta Empire, the Kara-Kitai Khanate, the Corasmian Empire or the Song Dynasty in the south of China.