Taisun Khan (or Toghtoa Bukha, Toγtoγa Buqa; Modern Mongolian:Taisun haan) (1416–1453) was a Khagan of the Northern Yuan dynasty based in Mongolia. He was enthroned as Khagan of the Great Yuan. Under his nominal rule, the Oirats successfully reunited the Mongol tribes and threatened the Ming dynasty to their south for the first time since the Battle of Kherlen in 1409.

After the previous khan Oyiradai's death in 1425 an internecine war lasting several years broke out among the Oirats under Mahamud (Bahamu, Batula) and western Mongol clans led by Gulichi's family. The central and eastern Mongol clans, in the meantime, proclaimed Adai Khan as the great khan shortly after Oyiradai's death in 1425.

Toghtoa Bukha was the eldest son of Ajai who was a posthumous birth of Elbeg Khan (d.1399) and Öljeitü the Beauty. While wandering with his brothers in western Mongolia, Toghtoa Bukha met Mahamud's son and successor, Toghan Taishi of the Four Oirats. The latter married him to his daughter and wanted to use him as pawn. The Oirats crowned Toghtoa Bukha as their own khagan in 1433. This resulted in half a decade of simultaneous existence between two khans supported by opposing Mongol clans.

Toghtoa Bukha Khan was an ambitious leader who aspired to gain real power and regaining the former glory of the Yuan Dynasty. His ambitions inevitably lead to a conflict of interests with powerful Oirat nobles. Although the Oirats shared the same ambition of recovering the glory of Genghis Khan with the new khan, they were well aware of the fractured nature of the Mongol tribes. To buy time before being able to unite them, they first needed to make peace with the Ming dynasty. The Oirats were careful not to enrage the Ming by not officially proclaiming the Yuan and thereby obtained help from the Ming court in defeating the Khorchin. Adai Khan of the Khorchin was killed in 1438.

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