Frederick William, elector of Brandenburg, usually styled the Great Elector, and the founder of the Prussian monarchy, born in 1620, died in Potsdam, April 29, 1688. He came to the electoral power at the age of 20 (1640), on the death of his father, George William, the 10th elector. The father had been a feeble prince, with a traitorous minister. His estates had for many years been ravaged by the contending parties in the thirty years' war. The cities lav almost in ruins, the vil-lages had been for the most part burned and depopulated, and a part of his paternal inheritance had been confiscated by the Swedes. The young prince began his reign by dismissing his father's unworthy council, regulating his finances, and negotiating with so much address as to regain his lost provinces, which were guaranteed to him by the peace of Westphalia eight years later. A year after his accession he concluded a treaty of neutrality with the Swedish queen Christina, and three years after, by an armistice with Hesse-Cassel, the strong outpost city of Cleves and the county of Mark in Westphalia were added to his dominions.

Under the treaty of W'estphalia (1648) the elector, who had just claims to the whole of Pomerania, received only the eastern portion of that country; but as an indemnification for the loss of the western division and the island of Rugen, he obtained the county of Hohenstein, the bishoprics of Minden, Halberstadt, and Kamin, as lay principalities, and the reversion of the archbishopric of Magdeburg. After the conclusion of the peace, Frederick William directed his attention to the organization of a standing army, and after a few years he had an army of 25,000, disciplined according to the Swedish system. He formed an alliance with Charles X. of Sweden in 1655 against Poland. The sequel was the fall of Warsaw, and Frederick's achievement of the independence of his Prussian duchy, formerly under enfeoffment to Poland. Louis XIV. at this time was pursuing his project of a Rhine frontier and the conquest of the Spanish Netherlands. He seized a line of frontier towns, and invaded Holland (1672). Of the German princes, the elector of Brandenburg alone seemed conscious of the danger, and after arming his exposed West-phalian dominions he appealed successfully to the emperor Leopold I., to Denmark, to Hesse-Cassel, and other German states.

A joint army was placed under the command of an imperial general; but the imperial cooperation was crippled through the machinations of Leopold's privy councillor, Lobkowitz, who became a secret tool of the French ministers. Frederick William was compelled thus to come to terms with France, with the loss of Wesel and Rees (1673). Immediately after this event, Leopold resuming operations against the French, the elector again took up arms, and Louis, in orde,r to keep the electoral forces occupied in their own country, engaged the king of Sweden to advance upon Berlin. The Swedes accordingly entered Brandenburg by a rapid forced march. Frederick William arrived suddenly from the Rhine at Magdeburg, and hurrying across the Elbe at the head of his cavalry (only 6,000 in number), surprised the Swedes at Fehrbellin. His infantry (11,000) were many miles in the rear, but he attacked the enemy without delay, June 18, 1675. The rout was complete. Frederick pursued the flying enemy into Pomerania, and reduced the greater portion of the province. By the treaty of St. Germain, June 29, 1679, the elector restored nearly all his conquests, and received from France 300,000 crowns. He now devoted himself to the prosperity of his dominions and the extension of their area.

He founded universities, welcomed 20,000 Protestant exiles whom Louis XIV. banished from France, and made it the aim of his life to oppose French aggression and to protect the liberties of Germany.