Mamai, holding military rank of Commander of 10,000 troops (Division General) - "tumenbashy" ("temnik" in Russian), was not a member of ruling Mongol dynasty. In 1378 - 1380 he tried to force Russianss to pay annual tribute to him instead of Golden Horde.
After being heavely defeated by Russians in 1380 on Kulikovo Field Mamai was assassinated in Kaffa (Crimea) by Genoeses, who could not forgive the total waste of military unit of Genoese crossbow archers slauthered by Russians.
One of his sons lately escaped in Lithuania, and, serving for Grand Prince Vitautas received title of Prince of Glina with multiple estates around modern site of Poltava (Ukraine)in early 1400s. In the very beginning of 16th century this family (Slavicized and Bapticized by that time) moved on Muscovite service. Eventually, in 1520s Princess Elena Glinskay became wife of Vassily III, Grand Prince of Moscow, and mother of Ivan the Terrible