John III (John Sobieski)sôbyĕˈskē, 1624–96, king of Poland (1674–96), champion of Christian Europe against the Ottomans. Born to an ancient noble family, he was appointed (1668) commander of the Polish army. He defeated (1673) the Ottomans at Khotin shortly after the death of King Michael, and in 1674 he was elected to succeed Michael. John's plans to recover East Prussia led him to conclude alliances with France (1675) and Sweden (1677) against Frederick William of Brandenburg (the Great Elector). However, the emphasis of his foreign policy changed when Sultan Muhammad IV and the Hungarians under Thököly advanced against Austria. Realizing the danger to all Europe, John allied (1683) with Holy Roman Emperor Leopold I and, leading combined imperial and Polish forces, raised the siege of Vienna and defeated the much larger Ottoman army under Kara Mustapha. Despite Leopold's ungrateful reception, John continued his campaign and pursued the Ottomans into Hungary. In 1684 he formed a Holy League with the pope, the emperor, and Venice. In 1686 he made a treaty with Russia that confirmed Russian suzerainty in E Ukraine. However, John's attempts (1684–91) to secure access to the Black Sea by wresting Moldavia and Walachia from the Ottoman Empire were unsuccessful. His loss of military prestige encouraged the nobles to oppose him at home. John's death, followed by the choice of the elector of Saxony as King Augustus II of Poland, marked the virtual end of Polish independence.