Casimir III the Great (Kazimierz Wielki; April 30 1310 – November 5, 1370), last King of Poland from the Piast dynasty (1333–1370), was the son of King Władysław I the Elbow-high and Jadwiga of Gniezno and Greater Poland.
Born in Kowal, Casimir (Kazimierz) the Great first married Anna, or Aldona Ona, the daughter of the prince of Lithuania, Gediminas. The daughters from this marriage were Cunigunde (d 1357), who was married to Louis VI the Roman, the son of Louis IV, Holy Roman Emperor, and Elisabeth, who was married to Duke Bogislaus V of Pomerania. Aldona died in 1339 and Kazimierz then married Adelheid of Hesse. He divorced Adelheid in 1356, married Christina, divorced her, and while Adelheid and possibly also Christina were still alive ca. 1365 married Hedwig (Jadwiga) of Głogów and Sagan.
His three daughters by his fourth wife were very young and regarded as of dubious legitimacy because of their father's bigamy. Because all of the five children he fathered with his first and fourth wife were daughters, he would have no lawful male heir to his throne.
Kazimierz the Great built many new castles, reformed the Polish army and Polish civil and criminal law. At the Sejm in Wiślica, March 11, 1347, he introduced salutary legal reforms in the jurisprudence of his country. He sanctioned a code of laws for Great and Lesser Poland, which gained for him the title of "the Polish Justinian" and founded the University of Kraków which is the oldest Polish university, although his death temporary stalled the university's development (which is why it is today called the "Jagiellonian" rather than "Casimirian" University).
He organized a meeting of kings at Kraków (1364) in which he exhibited the wealth of the Polish kingdom.
In order to enlist the support of the nobility, especially the military help of pospolite ruszenie, Kazimierz was forced to give up important privileges to their caste, which made them finally clearly dominant over townsfolk (burghers or mieszczanstwo).
In 1335, in the "treaty of Trenčín", Kazimierz relinquished "in perpetuity" his claims to Silesia. In 1355 in Buda Kazimierz designated Louis of Anjou (Louis I of Hungary) as his successor. In exchange, the szlachta's tax burden was reduced and they would no longer be required to pay for military expeditions expenses outside Poland. Those important concessions would eventually lead to the ultimately crippling rise of the unique nobles' democracy in the Polish–Lithuanian Commonwealth.
His second daughter, Elisabeth, Duchess of Pomerania, bore a son in 1351, named Kasimir (Kazimierz of Pomerania) after his maternal grandfather. He was slated to become the heir, but did not succeed to the throne, dying childless in 1377, 7 years after King Kazimierz. He was the only male descendant of King Kazimierz who lived during his lifetime.
Also, his son-in-law Louis VI the Roman of Bavaria, Margrave and Prince-elector of Brandenburg, was thought as a possible successor as king of Poland. However, he was not deemed eligible as his wife, Kazimierz's daughter Cunigunde, had died already in 1357, without children.
Kazimierz had no legal sons. Apparently he deemed his own descendants either unsuitable or too young to inherit. Thus, and in order to provide a clear line of succession and avoid dynastic uncertainty, he arranged for his sister Elisabeth, Dowager Queen of Hungary, and her son Louis king of Hungary to be his successors in Poland. Louis was proclaimed king on Kazimierz's death in 1370, and Elisabeth held much of the real power until her death in 1380.
Many of the influential lords of Poland were unsatisfied with the idea of any personal union with Hungary, and 12 years after Kazimierz's death, (and only a couple of years after Elisabeth's), they refused in 1382 to accept the succession of Louis's eldest surviving daughter Mary (Queen of Hungary) in Poland too. They therefore chose Mary's younger sister, Hedwig, as their new monarch, and she became "King" (=Queen Regnant) Jadwiga of Poland, thus restoring the independence enjoyed until the death of Kazimierz, twelve years earlier.
King Kazimierz was favorably disposed toward Jews. On 9 October 1334, he confirmed the privileges granted to Jewish Poles in 1264 by Bolesław V the Chaste. Under penalty of death, he prohibited the kidnapping of Jewish children for the purpose of enforced Christian baptism. He inflicted heavy punishment for the desecration of Jewish cemeteries.
Although Jews had lived in Poland since before the reign of King Kazimierz, he allowed them to settle in Poland in great numbers and protected them as people of the king.
Aldona died on 26 May, 1339. Casimir remained a widower for two years. On 29 September, 1341, Casimir married his second wife Adelheid of Hesse. She was a daughter of Henry II, Landgrave of Hesse and Elisabeth of Meissen. Her maternal grandparents were Frederick I, Margrave of Meissen and his second wife Elizabeth of Lobdeburg-Arnshaugk. They had no children.
Casimir started living separately from Adelheid soon after their marriage. Their loveless marriage lasted until 1356. Casimir effectively divorced Adelheid and married his mistress Christina. Christina was the widow of Miklusz Rokiczani, a wealthy merchant. Her own origins are unknown. Following the death of her first husband she had entered the court of Bohemia in Prague as a lady-in-waiting. Casimir brought her with him from Prague and convinced the abbot of the Benedictine abbey of Tyniec to marry them. The marriage was held in a secret ceremony but soon became known. Adelheid renounced it as bigamous and returned to Hesse without permission.
Casimir continued living with Christine despite complains by Pope Innocent VI on behalf of Adelheid. The marriage lasted until 1363/1364 when Casimir again declared himself divorced. They had no children. In about 1365, Casimir married his fourth wife Jadwiga of Głogów and Sagan. She was a daughter of Henry III, Duke of Silesia-Żagań and Anna of Mazovia. They had three children:
With Adelheid still alive and Christine possibly surviving, the marriage to Jadwiga was also considered bigamous. The legitimacy of the three last daughters was disputed. Casimir managed to have Anna and Kunigunde legitimated by Pope Urban V on 5 December, 1369. Jadwiga the younger was legitimated by Pope Gregory XI on 11 October, 1371.
Casimir also had three illegitimate sons by his mistress Cudka, wife of a castellan.