For 10 points, name this Grand Duke of Lithuania known as "the Great," who defeated the Teutonic Order alongside his cousin Jogaila at the Battle of Grunwald.
This ruler legendarily saved the Karaites, whom he had resettled in his capital, from a flood by ordering his horse to drink the floodwaters. This ruler's attempt to restore Tokhtamysh to power as khan of the Golden Horde resulted in his defeat by Temür Qutlugh and Edigü at the Battle of the Vorskla River. This ruler recovered his father's lands, and finished his father's construction of the Trakai Island Castle after reconciling with his cousin through the Astrava Agreement. After being offered the crown of Bohemia, this ruler sent his nephew Sigismund Korybut to Bohemia as governor. The death of this son of Keştutis led to a civil war between supporters of his brother Sigismund and his cousin Švitrigaila. For 10 points, name this Grand Duke of Lithuania known as "the Great," who defeated the Teutonic Order alongside his cousin Jogaila at the Battle of Grunwald.
This ruler legendarily saved the Karaites, whom he had resettled in his capital, from a flood by ordering his horse to drink the floodwaters.
Vytautas the Great [or Vytautas Didysis or Witold Kiejstutowicz]