William I. (Wilhelm Friedrich Ludwig), king of Prussia and emperor of Germany, born March 22, 1797. He is a son of Frederick William III. and of the celebrated queen Louisa, and in early life accompanied the armies which overthrew Napoleon I. After the accession of his childless brother, Frederick William IV., in 1840, he became known as heir apparent and prince of Prussia; he was invested with high office and sat in the first united diet in 1847. Chiefly on account of his fondness for the army, he was regarded as an absolutist in March, 1848, and withdrew to England till June, when, the excitement in Berlin having subsided, he took a seat as a deputy in the national assembly. On June 12, 1849, an unsuccessful attempt was made upon his life at Nieder-Ingelheim, while he was on the way to Baden to take command of the Prussian forces. He put down the republican insurrection in a few weeks. Subsequently he was stationed at Coblentz as military governor on the Rhine and in Westphalia, and also became governor of the federal fortress of Mentz and grand master of the freemasons. On important occasions he was called to Berlin to confer on state affairs, and his loyal nature was soon generally recognized.

His brother being disabled by illness in 1857, he acted in his stead, and in October, 1858, was formally installed as regent; and he succeeded him as king on Jan. 2, 1861. In July another abortive but graver attempt upon his life was made at Baden-Baden by the student Oskar Becker, who charged him with incapacity to effect the union of Germany, the accomplishment of which, however, became the salient feature of his reign. With the assistance of Von Roon he paved the way for victory by the reorganization of the army, and in 1862 he placed Bismarck at the head of the cabinet as minister of foreign affairs. After procuring in 1864 the cooperation of Austria in the SchleswigHolstein war, he achieved a great victory, for Prussia, and the convention of Gastein (Aug. 14, 1865) assigned Schleswig temporarily to him, and Lauenburg permanently. His sagacity in selecting able ministers and generals was equalled only by his firmness in sustaining them against all opposition; and his confidence in Bismarck as well as in Von Roon and Moltke was fully confirmed by the rapid and brilliant success of the war of 1866 in conjunction with Italy against Austria, in which he personally took an active part, and which extinguished Austria as a German power, and placed him at the head of the new North German confederation, with Schleswig-Holstein, Hanover, Hesse-Cassel, Nassau, and Frankfort added to his Prussian dominions.

On Feb. 24, 1867, he opened the constituent Reichstag, and on July 1 he made Bismarck chancellor. In the preceding month he and his nephew, the emperor Alexander II. of Russia, had visited Napoleon III. on occasion of the Paris exposition. The friendly relations between Prussia and Russia were subsequently strengthened, the two chancellors, Bismarck and Gortchakoff, being as much in accord as the two monarchs; and this good understanding was of the greatest moment in the ultimate victory over France and the attainment of German unity. -The king also took every opportunity to vindicate the historic position of his dynasty as protector of the Protestant faith. The candidature of Prince Leopold of Hohenzollern for the Spanish throne, and the king's objections against further interviews with the French ambassador, Count Benedetti, who had repeatedly importuned him at Ems (July, 1870), became the pretext for the French declaration of war against Prussia. The South German states at once joined the North German confederation against France, under the lead of Prussia, and the war was a continuous series of prodigious victories. (See France.) William, accompanied by Bismarck, Von Roon, and Moltke, was with the German armies from the beginning to the end of the contest, and received at Sedan (Sept. 2) the surrender of Napoleon III. On Oct. 5 he fixed his headquarters in the palace of the former French kings at Versailles, and here, on Jan. 18, 1871, he was proclaimed emperor of Germany. After signing the preliminaries of peace, Feb. 26, he intimated to the emperor of Russia that Germany would never forget the service rendered by his strict neutrality.

The treaty was ratified on March 1 and 2, and the emperor left Versailles on the 7th. He entered Berlin on the 15th, and on the 21st opened the first Reichstag of the new empire. The definitive peace with France was signed at Frankfort May 10, and on June 9 appeared the emperor's proclamation incorporating Alsace-Lorraine with the empire. On Aug. 16, 1875, the emperor unveiled Bandel's colossal monument of the national hero Arminius, on the summit of the Grotenberg near Detmold. After exchanging visits with the emperor of Austria, he reached Milan on Oct. 18, to return the visit of the king of Italy, his good relations with Victor Emanuel being of special importance in view of the increasing magnitude of the emperor's contest with the Roman hierarchy. Early in 1876 he joined the emperors of Austria and Russia in the project of reform suggested to Turkey for the pacification of her revolted provinces. Monuments in his honor have been erected all over the empire. His life has been written by Schneider (4th ed., 1868) and Weisshuhn (8th ed., 1869). L. Schmidt has written his military history, embracing the years 1867-71 (Militärische Lebensbeschreibiing, Berlin, 1875-'6). By his wife, the empress Augusta (daughter of the grand duke Charles Frederick of Saxe-Weimar-Eisenach, born Sept. 30, 1811, and married June 11, 1829), he has one son, the crown prince (see Frederick William Nicholas Charles, vol. vii., p. 462), and one daughter, the princess Louisa, born Dec. 3, 1838, who married in 1856 the grand duke Frederick of Baden.