Casimir IV, 1427–92, king of Poland (1447–92). He became (1440) ruler of Lithuania and in 1447 succeeded his brother Ladislaus III Ladislaus III, 1424–44, king of Poland (1434–44) and, as Uladislaus I, king of Hungary (1440–44), son of Ladislaus II. He led two crusades against the Ottomans; the first (1443) was highly successful, but the second ended with his defeat and death
..... Click the link for more information. as king of Poland. He united the two nations more closely by placing them on an equal footing. With the Second Peace of Torun (1466) he ended a 13-year war against the Teutonic Knights Teutonic Knights or Teutonic Order (t
..... Click the link for more information. in his favor; Poland gained territories and the Knights accepted Polish suzerainty over the area they retained. Calling (1467) the first Polish diet, he confirmed the privileges of the aristocracy. His marriage to an Austrian Hapsburg enabled his son Ladislaus to become king of Bohemia and later king of Hungary as Uladislaus II. Casimir was succeeded by his sons John I (1492–1501), Alexander I (1501–5), and Sigismund I (1506–48).

Casimir IV

known as Casimir Jagiellonian Polish Kazimierz Jagiellonczyk

(born Nov. 30, 1427—died June 7, 1492) Grand duke of Lithuania (1440–92) and king of Poland (1447–92). He became ruler of Lithuania by will of the boyars and king of Poland on his brother's death. He sought to preserve the political union between Poland and Lithuania and to recover the lost lands of old Poland. Through his own marriage to Elizabeth of Habsburg and the marriages of his children, he formed alliances with various European royal houses and built the Jagiellon dynasty. The great triumph of his reign was the effective destruction of the Teutonic Order (1466), which brought Prussia under Polish rule.