Frederick William II., king of Prussia, born Sept. 25, 1744, died Nov. 16, 1797. He was the grandson of Frederick William I., nephew of Frederick the Great, and son of the prince Augustus William, who, having incurred the resentment of his brother the king by an unsuccessful retreat after the disastrous battle of Kolin (1757), shortly after died. Frederick William, having become heir presumptive to his uncle, received from him but rare marks of cordiality or affection, was rather austerely educated, and often exposed to all the dangers of the war during the last period of the seven years' struggle. He enjoyed little freedom in the second and peaceful half of Frederick's reign, was obliged to repudiate his first wife, Elizabeth of Brunswick, because of ill conduct, and lived in a circle of his own, in which some visionaries of the then powerfully organized sect of illuminati were particularly conspicuous, who maintained their influence over him even after his accession to the throne. This took place on Aug. 17, 1786. Freed from long restraint, the new king gave himself up without moderation to his voluptuous inclinations. Mistresses and favorites reigned in the court and squandered the treasures of the state.

He sought to gain the favor of the people by ostentatious mildness; even the discipline of the army was relaxed. The first important act of his policy abroad, which was but slightly influenced by the energetic minister Herzberg, was to reinstate in power his brother-in-law the stadtholder of the Netherlands, who had been deposed by the anti-Orange party. A Prussian army under the duke of Brunswick entered Holland, occupied Amsterdam, and restored the ancient order of things, which was confirmed by a treaty concluded in 1788, at the Hague, by Prussia, England, and Holland. Alarmed by the alliance of the emperor Joseph II. with Catharine II. of Russia, and by the successes of the Russians in the war against Turkey, he concluded a treaty with the latter power guaranteeing all its possessions. An army was assembled in Silesia, near the Bohemian frontier. Before the outbreak of the war, however, Frederick William wavered, and finally restored his good understanding with Austria by the treaty of Reichenbach (1790), concluded with the successor of Joseph, Leopold II., who soon also made peace with the Porte. Russia, however, was allowed to continue her operations undisturbed. Herzberg resigned.

The interview at Pilnitz with the emperor (1791) prepared the first coalition against the French revolution. The hostile operations began in the spring of 1792. The duke of Brunswick entered France in the summer; the king and the crown prince, the son of his second wife, Louisa of Hesse-Darmstadt, joined him there. Want of harmony and repeated blunders on the part of the allies, revolutionary fanaticism and the skill of the commanders on the side of the French, soon turned the scale in favor of the latter, compelling Frederick William to keep the defensive, and finally to conclude the treaty of Basel (1795) with the republic, in which he ceded his territories beyond the Rhine, contracting for future indemnities and a kind of protectorate over northern Germany. His participation in the affairs of Poland was productive of more advantageous results. Having encouraged the so-called long Polish diet in its efforts to regenerate the state and to make it independent of Russia, by a treaty in which he guaranteed its integrity (1790), he afterward, when engaged in the war with France, found it more convenient and profitable to share the prey with Russia and Austria. He marched his army into Poland, and actively promoted the second and third dismemberments of the unhappy republic (1793-'95). His share was large, extending to the Niemen, and including the capital, Warsaw. These wars and the extravagance of the court exhausted the finances of Prussia. Intolerant edicts and severe restrictions of the press contributed to make his reign unpopular; but it was not without merit in developing the resources of the state and the welfare of the people by useful internal improvements.

The judicial organization of Prussia was also greatly promoted under Frederick William. He completed and introduced the code of laws prepared by Frederick the Great.