Algirdas or Olgierd (Олгерд), b ca 1296, d May 1377. Prince of Krevo and Vitsebsk (1341–5) and grand duke of Lithuania (1345–77), son of Gediminas. With the assistance of his brother Kęstutis, the prince of Samogitia, Algirdas unified the Lithuanian territories and waged war to enlarge his realm, making it one of the largest European states of his day. In 1345, after capturing Vilnius, Algirdas became the grand duke of Lithuania. Thereafter, he gradually annexed the larger part of the Ukrainian territories. At first, in about 1355, Algirdas won the Chernihiv land and Novhorod-Siverskyi land from the Golden Horde. In 1363 he defeated the Tatar army at Syni Vody and annexed the Kyiv land. Soon after he added Podilia and the Pereiaslav land to his domain. Algirdas waged a successful war over Volhynia against the Polish king Casimir III the Great and left him with only the Belz land and the Kholm region in Ukraine. He also annexed the principality of Smolensk and extended his influence over Pskov and Novgorod the Great. Algirdas led campaigns against Moscow in 1368, 1370, and 1372 and helped his brother Kęstutis in the struggle against the Teutonic Knights.
Algirdas succeeded in unifying all of the Belarusian and most of the Ukrainian territories under the Grand Duchy of Lithuania. His respect for Ukrainian culture and the Ukrainian church won him the loyalty of the Ukrainian people as well as of the Ukrainian princes and magnates, who helped to administer the state. Algirdas left some of the Ukrainian territories he annexed under the care of the Ukrainian princes of the Riurykide dynasty; others he granted to his relatives. During his reign the Ukrainian (Ruthenian) language became an official language of the Grand Duchy of Lithuania.
[This article originally appeared in the Encyclopedia of Ukraine, vol. 1 (1984).]