Vytautas the Great (Vitovt, Witold) (sometimes - Aleksandras I, in Belarusian as Vitaut (Вітаўт)) 1352-1430 was Lithuanian grand duke, ruler of the Grand Duchy of Lithuania. He was the son of Kęstutis, cousin of Ladislaus II of Poland (Jagiełło, Jogaila), grandfather of Vasili II of Russia.

He was prince of Hrodno 1370-1382, prince of Lutsk 1378-1389. In 1373-1382 he waged war against Jogaila, backing his father Kestutis. He was defeated and imprisoned, but he was able to escape to the Teutonic knights in 1382. After participating in several raids against Jogaila, he reconciliated with him later and participated in the signing of Union of Krewo with Poland in 1385, and was baptised in 1386 in the Catholic rite (he was also earlier baptised in the Orthodox rite), receiving the name Alexander.

Later he escaped to Teutonic knights twice, until finally he became governor of Lithuania in 1392. He conducted his own policy there, and he got support from pope Boniface IX for organising a crusade against Mongols. After being defeated by the Golden Horde at the Battle of Vorskla in 1399, he again improved relations with Poland, resulting in the union of Vilnius-Radom in 1401. He received the title of Grand Duke of Lithuania in the same year. He conquered Smolensk in 1404 and waged a war in 1406-1408 against Muscovy, ending in peace at Ugra. He also backed an uprising against the Teutonic Order in Samogitia. In 1410 he commanded the Lithuanian army in the battle of Grunwald (also called the battle of Tannenberg or Žalgirio mūšis). As a result of the First Treaty of Torun in 1413, he received Samogitia (Lower Lithuania) for his lifetime (Only after another war with the Teutonic Order in 1422, Samogitia was returned to Lithuania for eternal times). He was one of the creators of union of Horodlo with Poland (1413).

He backed economic development of his state and introduced many reforms. Under his rule Lithuania slowly became more centralised, as local princes were replaced by the duke's governors. He tried to receive the title of king with the backing of Sigismund, Holy Roman Emperor, but the envoys who were transporting the crown were stopped by Polish magnates in 1429.