Frederick III., surnamed the Pacific, fourth emperor of Germany of the house of Hapsburg (Frederick IV. as king of Germany, and V. as archduke of Austria), son of Duke Ernest of Styria and a Polish princess, born in Innspruck, Sept. 21, 1415, died in Linz, Aug. 19, 1493. He began his reign over Styria, Carinthia, and Carniola, together with his brother Albert the Prodigal, in 1435, became after the death of the emperor Albert II. (1439) guardian of his son Ladislas the Posthumous, and was unanimously elected to the throne of Germany in 1440, and crowned at Aix-la-Chapelle in 1442. Possessed of many private virtues, he was nevertheless inadequate to the task of ruling the German empire in that period of anarchical turbulence, or even of defending the interests of his house against the attacks of the warlike and ambitious Matthias Corvinus, king of Hungary, George Podiebrad of Bohemia, and Charles the Bold of Burgundy. The only weapon he seems to have wielded with dexterity was diplomacy, but this, too, served only the private purposes of the house of Austria, of which he may be regarded as the second founder. Wars, however, in which his part was generally passive, filled nearly the whole reign of this peace-loving monarch, which was the longest of any German emperor's, lasting for 53 years.

His brother Albert, duke of Upper Austria, repeatedly attacked him; the Hungarians under John Hunyady invaded Austria (1445-'52); the Armagnacs, whom the emperor had called to aid him against the Swiss, committed depredations (1445); Matthias Corvinus and George Podiebrad defeated the imperial forces; the Turks ravaged Carniola (1469); hostilities broke out with Charles the Bold of Burgundy, and a war was carried on in the Netherlands, which Maximilian, the son of Frederick, had received after the death of Charles the Bold (1477) with the hand of his daughter Mary, and where he was made captive in 1488. Frederick was also humiliated by the usurpation of Sforza at Milan (1447), after the death of the last Visconti; by the Swiss, who routed the Armagnacs, and compelled him to an unfavorable treaty (1449); in the quarrel of the succession of the Palatinate (1449), which threatened to cost him his throne; by continual lawlessness in Germany, where he was once cited before the secret tribunal of the Vehme; and by the successive encroachments of the popes, particularly of Pius II. (once his secretary as Aeneas Sylvius). His chief efforts to avert the invasion of the Turks were a journey to Rome for a conference with the pope (1468), and the convening of a diet at Ratisbon (1471), both without result.

In 1485 Frederick had a new quarrel with Matthias, who wrested from him Vienna and all Lower Austria. On the death of Matthias (1490), Frederick regained these possessions, and his last years were cheered by the successes of his son Maximilian, whom he had made king of Rome (1480), and finally intrusted with all the cares of his dominion (1490), himself retiring to Linz, where he was engaged in his favorite studies of astrology, alchemy, and botany till the end of his life. He was the last king of Germany who was crowned emperor of Rome and king of the Lombards. Having inherited Lower Austria on the death of Ladislas, and Upper Austria on that of his brother Albert, he raised these united provinces to the dignity of an archduchy. The crown of Germany became nearly hereditary in his house, the next successor being his son Maximilian I. His device is said to have been A. E. I. 0. U.: A ustrioe est imperare orbi unirerso. A collection of his sayings was published under the title of Margarita Facetiarum (Strasburg, 1509).