Algirdas (, , , name on his personal seal (Cyrillic Script) Олгер equals to Holger) (c. 1296 – May 1377) was a monarch of medieval Lithuania. He ruled the Lithuanians and Ruthenians from 1345 to 1377. With the help of his brother Kęstutis (who defended the western border of the Duchy) he created an empire stretching from the present Baltic states to the Black Sea and to within fifty miles of Moscow.