Bolesław Januszowic

Bolesław Januszowic (; 1385/86 – ca. 4 May 1424 ), was a Polish prince and member of the House of Piast.

He was the second son of Duke Janusz I of Warsaw and Danutė of Lithuania, a daughter of Kęstutis.

Life From an early age he was prepared to take over the government in Masovia, alongside his older brother Janusz the Younger. In 1409 he was sent by his father at the head of a retaliatory expedition against the Teutonic Order, culminating with the conquest and burning of Działdowo and 14 surrounding villages. Bolesław married the Lithuanian princess Anna (d. 25 May 1458 in Czersk), a daughter of Feodor Olgerdovich, Prince of Rylsk, Ratnie and Bryansk, one of the eldest sons of Algirdas, Grand Duke of Lithuania, and in consequence, a half-brother of King Władysław II Jagiełło (born from Algirdas' second marriage). They had three children:

Konrad (1413 - 21 July 1427). Euphemia (bef. 1420 - bef. 3 March 1436), married before 7 February 1435 to Michael Žygimantaitis, a Lithuanian prince. Bolesław IV (ca. 1421 - 10 September 1454), who succeeded his grandfather Janusz I in all his domains as his only surviving male descendant.