Mongol khan, or chief, who terrorized China during the 16th century. He converted the Mongols to the reformed, or Dge-lugs-pa (Yellow Hat), sect of Tibetan Buddhism.

Altan became chief of the eastern Mongols in 1543 and thereafter posed a constant threat to the northern borders of China under the Ming dynasty (1368–1644). In 1550 he led his forces across the Great Wall, which marked China's northwest border, and raided the outskirts of the capital at Peking. But he was forced to withdraw back into Mongolia a few days later.

Altan soon began his effort to create a stable system of government in his homeland. Using captured Chinese deserters, he set up a bureaucratic administration in the Chinese style, establishing his capital at Kuku-khoto (“Blue City”), just beyond the Great Wall. He also concluded a peace treaty with the Chinese in 1571, under which Altan was allowed to exchange horses for textiles. The Chinese also honoured him with the title of Shun-i Wang (“Obedient and Righteous Prince”).

In 1580 Altan was host to the head of the Dge-lugs-pa. Yellow Hat Buddhism was made the official religion under Altan's rule, and the head of the sect was given the title of Dalai Lama, a title implying spiritual primacy. Altan's own grandson became the new Dalai Lama when the head of the Dge-lugs-pa died. With Mongol military aid, later Dalai Lamas crushed the more established Karma-pa (Red or Black Hat) sect in Tibet and became the spiritual and, finally, temporal rulers of that country.