Bona Sforza in the context of "Barbara Radziwiłł"

Sigismund II Augustus (Polish: Zygmunt II August, Lithuanian: Žygimantas Augustas; 1 August 1520 – 7 July 1572) was King of Poland and Grand Duke of Lithuania, the son of Sigismund I the Old, whom Sigismund II succeeded in 1548. He was the first ruler of the Polish–Lithuanian Commonwealth and the last male monarch from the Jagiellonian dynasty.

Sigismund was elder of two sons of Italian-born Bona Sforza and Sigismund the Old, and the only one to survive infancy. From the beginning he was groomed and extensively educated as a successor. In 1529 he was chosen as king in vivente rege election while his father was still alive. Sigismund Augustus continued a tolerance policy towards minorities and maintained peaceful relations with neighbouring countries, with the exception of the Northern Seven Years' War which aimed to secure Baltic trade. Under his patronage, culture flourished in Poland; he was a collector of tapestries from the Low Countries and collected military memorabilia as well as swords, armours and jewellery. Sigismund Augustus' rule is widely considered as the apex of the Polish Golden Age; he established the first regular Polish navy and the first regular postal service in Poland, known today as Poczta Polska. In 1569, he oversaw the signing of the Union of Lublin between Poland and the Grand Duchy of Lithuania, which formed the Polish–Lithuanian Commonwealth and introduced an elective monarchy.

Gian Galeazzo Sforza (20 June 1469 – 21 October 1494), also known as Giovan Galeazzo Sforza, was the sixth Duke of Milan. He was the father of Bona Maria Sforza, who later became Queen of Poland. He died in 1494 aged 25 and was succeeded by his uncle, Ludovico Sforza.

Isabella Jagiellon (Hungarian: Izabella királyné; Polish: Izabela Jagiellonka; Lithuanian: Izabelė Jogailaitė; 18 January 1519 – 15 September 1559) was a princess of the Kingdom of Poland and of the Grand Duchy of Lithuania, and later also the Queen consort of Hungary. She was the oldest child of Sigismund I the Old, King of Poland and Grand Duke of Lithuania, and his Italian wife Bona Sforza.

In 1539, she married John Zápolya, Voivode of Transylvania and King of Hungary. At the time Hungary was contested between Ferdinand of Austria who wanted to add it to the Habsburg domains (see Royal Hungary), local nobles who wanted to keep Hungary independent (see Eastern Hungarian Kingdom), and Sultan Suleiman the Magnificent who saw it as a vassal state of the Ottoman Empire (see also Little War in Hungary). While Isabella's marriage lasted only a year and a half, it did produce a male heir – John Sigismund Zápolya born just two weeks before his father's death in July 1540.

The Volok Reform (Lithuanian: Valakų reforma; Belarusian: Валочная памера; Polish: reforma włóczna) was a 16th-century land reform in parts of the Grand Duchy of Lithuania (Lithuania proper, Duchy of Samogitia and parts of White Ruthenia). The reform was started by Grand Duchess Bona Sforza in her possessions to increase the revenues of the state treasury but soon was expanded statewide and was copied by other nobles and the Church. The reform increased effectiveness of agriculture by establishing a strict three-field system for crop rotation. The land was measured, registered in a cadastre, and divided into voloks (land unit of about 21.38 hectares (52.8 acres)). Volok became the measurement of feudal services. The reform was a success in terms of the annual state revenue that quadrupled from 20,000 to 82,000 kopas of Lithuanian groschens. In social terms, the reform and the accompanying Third Statute of Lithuania (1588), promoted development of manorialism and fully established serfdom in Lithuania which existed until the emancipation reform of 1861. The nobility was clearly separated from the peasants which severely limited social mobility.

The Neapolitan sums (Polish: Sumy neapolitańskie) refers to a loan made in 1557 by Bona Sforza, dowager Queen of Poland and Grand Duchess of Lithuania, to Philip II of Spain. The debt was never repaid and continued to be disputed between the Polish–Lithuanian Commonwealth and Kingdom of Spain up until the Third Partition in 1795. The phrase sumy neapolitańskie became synonymous in the Polish language with empty promises to repay debt.

Marie Louise Gonzaga (Italian: Maria Luisa, Polish: Ludwika Maria, Lithuanian: Liudvika Marija; 18 August 1611 – 10 May 1667) was Queen of Poland and Grand Duchess of Lithuania by marriage to two kings of Poland and grand dukes of Lithuania, brothers Władysław IV and John II Casimir. Together with Bona Sforza (1494–1557), she is regarded as one of the most influential and powerful queen consorts of the Kingdom of Poland and the Polish–Lithuanian Commonwealth.

Born in Nevers to Charles I, Duke of Mantua and Catherine of Guise, Marie was brought up at the French court as the future bride of Duke Gaston of Orléans. In 1645, she married Władysław IV of Poland with whom she did not have a harmonious relationship. After his death in 1648, the widowed queen married his half-brother and successor, John II Casimir. Marie Louise exercised considerable influence over her second husband and dictated the political course in the country. An ambitious and energetic woman, she was a strong supporter of an absolute monarchy for which she was reviled by certain spheres of the Polish szlachta and Lithuanian nobility. She, nevertheless, remained active in the Commonwealth's politics and co-sponsored the foundation of the first Polish newspaper, Merkuriusz Polski Ordynaryjny (Polish Mercury Ordinary), in 1661 as well as other public institutions.