Dayan Khan's empire in 1540
Dayan Khan was ruler of the Chagatai Khanate from 1498 to 1551, and of the Northern Yuan from 1537 to 1551. A descendant of Genghis Khan via his second son Chagatai, he had a remote claim to supremacy over the Mongols, which he exercised in his ambitions to reunite the broken Mongol Empire.
Although it had started out as one of the weakest Mongol khanates, the Chagatai Khanate alone had remained in one piece as the others were torn apart by civil wars or were overthrown by native dynasties. By 1388 its political structure had been strengthened thanks to the efforts of the warlord Timur, and from then on the Chagataid khans were able to start looking outwards once more and dream of returning to their past glories.
In 1537 Dayan Khan campaigned against the Oirats and the Buryats of Mongolia, defeating them and forcing them to swear loyalty to him. Soon after he gained the submission of the khan of the Northern Yuan, who was descended from Genghis' youngest son Tolui. When the younger khan died, Dayan took his place directly rather than appointing a successor, thus reuniting into one realm the whole of the Asiatic Steppes.
This is commonly thought of as the beginning of the Great Altaic Confederation. Dayan Khan's successors continued to expand the empire north and east, so that today Altai consists of the entirety of central and northern Asia.