Casimir III the Great, born on 30 April 1310 in Kowal, Kuyavia, was the third son of Władysław I Łokietek and Jadwiga of Kalisz. He had two brothers who died in infancy and three sisters. His father, a powerful prince, ruled over much of Lesser Poland and Kujawy, including Kraków. Following the deaths of the Bohemian kings Wenceslaus II and Wenceslaus III, Władysław sought to reclaim the Polish crown, which was claimed by John of Luxembourg after 1311. Władysław succeeded in uniting much of Poland and was crowned king in Kraków on 20 January 1320. Casimir married Aldona Anna, a Lithuanian princess, on 16 October 1325.Casimir's early life included a diplomatic mission to Hungary, where he became involved in a scandal involving Klára Záh, leading to violent repercussions. Poland faced military challenges from the King of Bohemia and the Teutonic Order, resulting in territorial losses. In 1331, Casimir was appointed governor of Greater Poland and Kuyavia, participating in military campaigns. Upon his father's death on 2 March 1333, Casimir ascended to the throne without major opposition and was crowned on 25 April 1333.His reign began under difficult circumstances, with John of Luxembourg still claiming the Polish crown. Casimir extended a truce with the Teutonic Order and sought alliances, notably with Hungary. He negotiated a marriage alliance for his daughter with the Holy Roman Emperor's son, which led to a peace agreement with the Luxembourgs. In 1335, a settlement was reached that returned some territories to Poland while Casimir renounced claims to others.Casimir focused on rebuilding and fortifying the kingdom, constructing numerous towns and castles. He established the Crown of the Polish Kingdom, ensuring the lands were recognized as independent from the monarchy. He reformed the judicial system, introducing civil and criminal codes, and founded the University of Kraków in 1364, the oldest university in Poland.Under his rule, Casimir expanded the kingdom, notably conquering Galicia–Volhynia, which provided access to Black Sea trade routes. In 1355, he designated his nephew Louis I of Hungary as his successor, as he had no legitimate sons. Casimir had five daughters and attempted to adopt his grandson, but this was invalidated after his death on 5 November 1370. Louis I succeeded him, marking the end of the Piast dynasty's rule in Poland.Casimir's reign was characterized by efforts to balance the power of the nobility, clergy, and bourgeoisie, earning him the nickname 'the Peasants' King.' He confirmed privileges for Jews, allowing them to settle in Poland and protecting their rights. His marriages included Aldona of Lithuania, Adelaide of Hesse, Krystyna Rokiczana, and Hedwig of Żagań, with whom he had three daughters. Casimir III the Great is remembered for his significant contributions to the development of Poland during his reign.