In the late 1370s and early 1380s, Timur helped Tokhtamysh assume supreme power in the White Horde against Tokhtamysh's uncle Urus Khan. After this he united the White and Blue Hordes, forming the Golden Horde, and launched a massive military punitive campaign against the Russian principalities between 1381 and 1382, restoring Turco-Mongol  power in Russia after the defeat in the Battle of Kulikovo. The Golden Horde, after a period of anarchy between the early 1360s and late 1370s, passed for a briefly reestablishing as a dominant regional power, defeating Lithuania in Poltava around 1383. But Tokhtamysh had territorial ambitions in Persia and Central Asia, and on account of this he turned against his old ally, Timur.
Question: Who led the White Horde before Tokhtamysh gained power?
Answer: Urus Khan