John III Sobieski - engraving by Carel Allardt

(born Aug. 17, 1629, Olesko, Pol. — died June 17, 1696, Wilanów) Elective king of Poland (1674 – 96). Named commander in chief of the Polish army (1668), he distinguished himself by victories over the Cossacks and Turks. His reputation was so great that he was elected king in preference to the Habsburgs' candidate. In 1683 he concluded a treaty with Emperor Leopold I against the Ottoman Turks. When a Turkish army approached Vienna later that year, he rushed there with troops, took command of the entire relief force, and achieved a brilliant victory, briefly restoring the kingdom of Poland-Lithuania to greatness for the last time. He was unsuccessful in a Hungarian campaign (1683 – 91) to liberate Moldavia and Walachia from Ottoman rule. Later rebellion within his own family, with nobles fighting each other rather than the Turks, led finally to Poland's downfall in the 18th century.

Early life and career
(copied from Encyclopedia Britannica)

Sobieski's ancestors were of the lesser nobility, but one of his great-grandfathers was the famous grand-hetman (military commander) St. Zólkiewski, and, when John was born, his father, James (Jakób) (1588–1646), had already taken a step to the higher ranks, sharing an office on the royal court. At the end of his life, the father even became castellan of Kraków, an office that secured him the highest rank among the members of the Polish Senate, or first chamber of the parliament.

John was well educated and toured western Europe in his youth, as was usual for a Polish noble of his class. When the Swedes invaded Poland in 1655, he joined them in opposition to the Polish king John Casimir. The following year he changed sides again and became one of the leaders in the fight to expel the Swedes. In 1665, through the influence of his patroness, Queen Maria Louisa (Ludwika), he was appointed to the prestigious office of grand marshal. In 1666 he became field commander of the Polish army. In October 1667 he defeated the Tatars and the Cossacks near Podhajce (now Podgaytsy, in Ukraine), and in the spring of 1668, when he triumphantly returned to Warsaw, he was named commander in chief. In 1665 he had married an ambitious young French widow, Marie-Casimire de la Grange d'Arquien (Marysienka). Marysienka planned to have John elected king after King John Casimir's resignation in 1668. When this plan failed—the nobility elected Michael Wisniowiecki in 1669—she began working to obtain support from Louis XIV of France for her husband's advancement. Since they were often separated—the husband on the front, his wife on journeys to France—Sobieski wrote long letters to Marysienka, which are now a highly interesting and important historical source. Her letters have not been preserved.

During the short reign of King Michael (1669–73), Sobieski distinguished himself by further victories over the Cossacks, and simultaneously he tried to undermine Michael, whose policies favoured the Habsburgs against France. Michael died in November 1673, and almost on the same day Sobieski won a splendid victory over the Turks under Hussein Pasa near Chocim (Hotin). Although this victory did not alter the disastrous conditions of the Peace of Buczacz concluded in 1672 (Poland had to cede territory to the Turks and to pay a considerable indemnity), Sobieski's reputation was so great that in May 1674 he was elected king in preference to the candidate backed by the Habsburgs.

At first Sobieski followed a pro-French policy. He tried to end the Turkish war by French mediation and concluded the secret Treaty of Jaworów with France (June 1675), in which he promised to fight the Holy Roman (Habsburg) emperor after the conclusion of peace with the Turks. In fact, only an armistice with them was concluded at Zórawno (October 1676), and the conditions were only slightly more favourable than those of Buczacz.

Sobieski's hopes of compensating for losses to the Turks in the southeast by using French and Swedish support to make territorial gains from Prussia in the northwest were also disappointed. Furthermore, Louis XIV was neither ready to recognize Marysienka's French relatives as members of a royal family nor willing to support the succession of Sobieski's son James (Jakób) to the Polish throne. The great nobles, especially those from Lithuania, were opposed to the French alliance because they feared that Sobieski was striving to attain absolute power with the help of France. It was becoming clear, moreover, that it was impossible to reconcile the interests of Poland and those of Louis, whose aim was to use Sobieski as an obedient vassal against the Habsburgs. Poland, for its part, had no differences with the Habsburgs and, after a series of Turkish attacks, came to regard the Ottomans, the allies of France, as its deadliest enemies.