John III Sobieski (Polish: Jan III Sobieski; Lithuanian: Jonas III Sobieskis; Latin: Ioannes III Sobiscius; 17 August 1629 17 June 1696) was King of Poland and Grand Duke of Lithuania from 1674 until his death in 1696.

Born into Polish nobility, Sobieski was educated at the Jagiellonian University and toured Europe in his youth. As a soldier and later commander, he fought in the Khmelnytsky Uprising, the Russo-Polish War and during the Swedish invasion known as the Deluge. Sobieski demonstrated his military prowess during the war against the Ottoman Empire and established himself as a leading figure in Poland and Lithuania. In 1674, he was elected monarch of the PolishLithuanian Commonwealth following the sudden and unexpected death of King Michael.

Sobieski's 22-year reign marked a period of the Commonwealth's stabilization, much needed after the turmoil of previous conflicts. Popular among his subjects, he was an able military leader, most famous for his victory over the Turks at the Battle of Vienna in 1683. The defeated Ottomans named Sobieski the "Lion of Lechistan", and the Pope hailed him as the saviour of Western Christendom. Suffering from poor health and obesity in later life, Sobieski died in 1696 and was buried at Wawel Cathedral in Krakw. He was succeeded by Augustus II of Poland and Saxony.

The szlachta (Polish: [ˈʂlaxta] (listen), exonym) were the noble estate of the realm in the Kingdom of Poland, the Grand Duchy of Lithuania, and the Polish–Lithuanian Commonwealth who, as a class, had the dominating position in the state, exercising extensive political rights and power. Szlachta as a class differed significantly from the feudal nobility of Western Europe. The estate was officially abolished in 1921 by the March Constitution.The origins of the szlachta are obscure and the subject of several theories.: 207  Traditionally, its members owned land (allods), often folwarks. The szlachta secured substantial and increasing political power and rights throughout its history, beginning with the reign of King Casimir III the Great between 1333 and 1370 in the Kingdom of Poland: 211  until the decline and end of the Polish–Lithuanian Commonwealth in the late 18th century. Apart from providing officers for the army, its chief civic obligations included electing the monarch and filling honorary and advisory roles at court that would later evolve into the upper legislative chamber, the Senate. The szlachta electorate also took part in the government of the Commonwealth via the lower legislative chamber of the Sejm (bicameral national parliament), composed of representatives elected at local sejmiks (local szlachta assemblies). Sejmiks performed various governmental functions at local levels, such as appointing officials and overseeing judicial and financial governance, including tax-raising. The szlachta assumed various governing positions, including voivode, marshal of voivodeship, castellan, and starosta.In 1413, following a series of tentative personal unions between the Grand Duchy of Lithuania and the Crown of the Kingdom of Poland, the existing Lithuanian-Ruthenian nobility formally joined the szlachta.: 211  As the Polish–Lithuanian Commonwealth (1569–1795) evolved and expanded territorially after the Union of Lublin, its membership grew to include the leaders of Ducal Prussia and Livonia. Over time, membership in the szlachta grew to encompass close to 10% of Polish-Lithuanian society, which made it as an electorate several times larger than most noble classes in other countries.

Despite often enormous differences in wealth and political influence, few distinctions in law existed between the great magnates and lesser szlachta. The juridic principle of szlachta equality existed because szlachta land titles were allodial, not feudal, involving no requirement of feudal service to a liege Lord. Unlike absolute monarchs who eventually took reign in most other European countries, the Polish king was not an autocrat and not the szlachta's overlord. The relatively few hereditary noble titles in the Kingdom of Poland were bestowed by foreign monarchs, while in the Grand Duchy of Lithuania, princely titles were mostly inherited by descendants of old dynasties. During the three successive Partitions of Poland between 1772 and 1795, most of the szlachta began to lose legal privileges and social status, while szlachta elites became part of the nobilities of the three partitioning powers.