KOSCIUSKO, or KOSCZIUSKO, THADDEUS (1746-1817), Polish patriot, was descended from an old family of small proprietors in the province of Lithuania, and was horn in 1746. From his father he inherited a taste for music, and in the other branches of education he showed such marked aptitude at the cadet school of Warsaw that along with some other youths he was sent at the expense of the state to complete his education at Versailles, Brest, and Paris. On his return to Poland he was appointed captain of artillery, but on account of the unfortunate result of his attachment to the daughter of a nobleman he in 1777 went to Paris, whence he sailed with the French fleet to aid the North American States in their war of independence. Under Washington he displayed great firmness and intrepidity in various trying circumstances, and rose to be general of a brigade. In 1786 he returned to his native country, where he lived in retirement until the reorganization of the army in 1789, when he was appointed major-general. In the war with Russia which followed the adoption of the new constitution of 1791 he conducted himself with conspicuous valour and skill, and at Dubienka, with a force of only 4000 men, held an army of 20,000 Russians at bay. All his efforts were however, rendered fruitless by the pusillanimity of King Stanislaus, who in March 1792 agreed to a humiliating peace, upon which Kosciusko along with several other leading officers resigned his commission. A second partition of Poland was consummated in August 1793, but a spirit of resistance gradually gathered force and culminated in the insurrection of 1794, when Kosciusko was recalled to Cracow and appointed generalissimo and dictator. With an army of 5000 he marched to meet the Russians, who were advancing upon Cracow in greatly superior numbers, and after a strenuous conflict of four hours'duration completely defeated them. On receipt of the intelligence Warsaw rose against the Russian authorities, putting 7000 persons to death ; and after instituting a new government Kosciusko went in pursuit of the enemy, who retired towards the Prussian frontiers. But for the interposition of Prussia the emancipation of Poland would have been accomplished. King Frederick William, however, advanced against Warsaw with an army of 40,000 men, to which Kosciusko could oppose only 15,000. He was defeated at Szezekocin, but retreated in good order upon Warsaw, which be defended with stubborn persistence, until the diversion of an insurrection in Great Poland caused them to raise the siege. Meantime an immense force of Russians was advancing against Warsaw in two divisions, the one under Suwaroff and the other under Fersen. Kosciusko resolved to attack Fersen before his junction with Suwaroff, but, as he had only 4000 men to meet the 14,000 Russians, his small army was in a few moments completely enveloped by superior numbers, and he himself fighting desperately fell pierced with several wounds. A tradition that as he fell lie gave utterance to the words "Finis Polonim" found currency several years afterwards, but when it came to his knowledge lie indignantly denied it. For two years he remained a prisoner at St Petersburg, but, gaining his liberty after the accession of Paul I., be went to England and then to America. Returning to France in 1798, he took up his residence at Fontainebleau. In 1806 he refused to allow Napoleon, whose professions he rated at their proper value, to use his name to incite a rising in Poland against Russia ; and the forged address put forth by Napoleon in his name was never accepted by his countrymen as genuine, although Kosciusko was unable to disavow it until eight years after it was issued. In 1814, when the Russian army entered France on the fall of Napoleon, Kosciusko had a long interview with the emperor Alexander of Russia, who, it is said, promised to him to restore to Poland its ancient boundaries. In 1815 he settled in Switzerland, devoting himself chiefly to agricultural pursuits. His death, October 17, 1817, was the result of an accidental fall from his horse. If as a statesman Kosciusko was more ardent than sagacious, he manifested a skill and daring as a soldier which but for the overwhelming nature of his task would have gained him a place among the most renowned generals of his time, while his noble and chivalrous patriotism, untainted by any desire after self-glorification, has secured him the world's universal admiration and esteem.

See the lives by Falkenstein (1827, 2d ed. 1834), Chodzko (1837), and Paszkowski (1872), and also Pologne et kussie, ljgencle do Kosciusko, by Jules Michelet (1851), reprinted in La Pologne martyr by the same author (1863).