Esen Taishi (died 1455) was a powerful Oirat Khagan of the Forty and the Four of Mongolia in the 15th century. He is best-known for capturing the Zhengtong Emperor in 1450 after the Battle of Tumu Fortress and reuniting briefly the Mongols. The Western Mongols reached their peak under his rule. Esentaish Khan was born in 1407, the red pig year. In the middle of the 17th century he united Oirats with Mongols and in 1452, the black monkey year, he became Khan of all Mongolia. He was a great commander who carried out the most proficient struggle against the Ming dynasty. But the had no imperial lineage and therefore he was overthrown by the nobility.