Title: Frederick William IV of Prussia
Content:  He was a Lutheran member of the Evangelical State Church of Prussia, a United Protestant denomination that brought together Reformed and Lutheran believers.
Title: Frederick William IV of Prussia
Content:  intervals. Despite being a devout Lutheran, his Romantic leanings led him to settle the Cologne church conflict by releasing the imprisoned Clemens August von Droste-Vischering, the Archbishop of Cologne. He also patronized further construction of Cologne Cathedral, Cologne having become part of Prussia in 1815. In 1844, he attended the celebrations marking the completion of the cathedral, becoming the first King of Prussia to enter a Roman Catholic house of worship. In 1842, on advice of Alexander von Humboldt, he founded the separate civil class of the Pour le Merite, the Order Pour le Mérite for Sciences and Arts (Orden Pour le Mérite für Wissenschaften und Künste). Said civil order is still being awarded today.
Title: Frederick William IV of Prussia
Content:  Frederick William IV (Friedrich Wilhelm IV.; 15 October 1795 – 2 January 1861), the eldest son and successor of Frederick William III of Prussia, reigned as King of Prussia from 7 June 1840 to his death on 2 January 1861. Also referred to as the "romanticist on the throne", he is best remembered for the many buildings he had constructed in Berlin and Potsdam as well as for the completion of the Gothic Cologne Cathedral. In politics, he was a conservative, who initially pursued a moderate policy of easing press censorship and reconciling with the Catholic population of the kingdom. During the German 
Title: Frederick William IV of Prussia
Content:  of 1848–1849, he at first accommodated the revolutionaries but rejected the title of Emperor of the Germans offered by the Frankfurt Parliament in 1849, believing that Parliament did not have the right to make such an offer. He used military force to crush the revolutionaries throughout the German Confederation. From 1849 onward he converted Prussia into a constitutional monarchy and acquired the port of Wilhelmshaven in the Jade Treaty of 1853. From 1857 to 1861, he suffered several strokes and was left incapacitated until his death. His brother (and heir-presumptive) Wilhelm served as regent after 1858 and then succeeded him as King.
Title: Frederick William, Elector of Brandenburg
Content:  Frederick William (Friedrich Wilhelm; 16 February 1620 – 29 April 1688) was Elector of Brandenburg and Duke of Prussia, thus ruler of Brandenburg-Prussia, from 1640 until his death in 1688. A member of the House of Hohenzollern, he is popularly known as "the Great Elector" (der Große Kurfürst) because of his military and political achievements. Frederick William was a staunch pillar of the Calvinist faith, associated with the rising commercial class. He saw the importance of trade and promoted it vigorously. His shrewd domestic reforms gave Prussia a strong position in the post-Westphalian political order of north-central Europe, setting Prussia up for elevation from duchy to kingdom, achieved under his son and successor.
Title: Frederick William II of Prussia
Content:  Frederick William II (Friedrich Wilhelm II.; 25 September 1744 – 16 November 1797) was King of Prussia from 1786 until his death in 1797. He was in personal union the Prince-elector of Brandenburg and (via the Orange-Nassau inheritance of his grandfather) sovereign prince of the Canton of Neuchâtel. Pleasure-loving and indolent, he is seen as the antithesis to his predecessor, Frederick the Great. (Frederick II). Under his reign, Prussia was weakened internally and externally, and he failed to deal adequately with the challenges to the existing order posed by the French Revolution. His religious policies were directed against the Enlightenment and aimed at restoring a traditional Protestantism. However, he was a patron of the arts and responsible for the construction of some notable buildings, among them the Brandenburg Gate in Berlin. Mozart, Haydn and Beethoven dedicated some of their works to him.
Title: Frederick William IV of Prussia
Content:  William was a staunch Romanticist, and his devotion to this movement, which in the German States featured nostalgia for the Middle Ages, was largely responsible for his developing into a conservative at an early age. In 1815, when he was only twenty, the crown prince exerted his influence to structure the proposed new constitution of 1815, which was never actually enacted, in such a way that the landed aristocracy would hold the greatest power. He was firmly against the liberalization of Germany and only aspired to unify its many states within what he viewed as a historically legitimate framework, inspired by the ancient laws and customs of the recently dissolved Holy Roman Empire. Frederick William opposed the idea of a unified German state, believing that Austria was divinely ordained to rule over Germany, and contented himself with the title of "Grand General of the Realm".
Title: Frederick William IV of Prussia
Content:  Born to Frederick William III by his wife Queen Louise, he was her favourite son. Frederick William was educated by private tutors, many of whom were experienced civil servants, such as Friedrich Ancillon. He also gained military experience by serving in the Prussian Army during the War of Liberation against Napoleon in 1814, although he was an indifferent soldier. He was a draftsman interested in both architecture and landscape gardening and was a patron of several great German artists, including architect Karl Friedrich Schinkel and composer Felix Mendelssohn. In 1823 he married Elisabeth Ludovika of Bavaria. Since she was a Roman Catholic, the preparations for this marriage included difficult negotiations which ended with her conversion to Lutheranism. There were two wedding ceremonies—one in Munich, and another in Berlin. The couple had a very harmonious marriage, but, after a single miscarriage in 1828, it remained childless. 
Title: Frederick William IV of Prussia
Content:  When revolution broke out in Prussia in March 1848, part of the larger series of Revolutions of 1848, the king initially moved to repress it with the army, but on 19 March he decided to recall the troops and place himself at the head of the movement. He committed himself to German unification, formed a liberal government, convened a national assembly, and ordered that a constitution be drawn up. Once his position was more secure again, however, he quickly had the army reoccupy Berlin and in December dissolved the assembly. He did, however, remain dedicated to unification for a time, leading the Frankfurt Parliament to offer him the crown of Germany on 3 April 1849, which he refused, purportedly saying that he 
Title: Frederick William III of Prussia
Content:  Prussia. The King's unsuccessful counterattack worsened tensions at the highest levels of government. The crown's aggressive efforts to restructure religion were unprecedented in Prussian history. In a series of proclamations over several years, the Church of the Prussian Union was formed, bringing together the majority group of Lutherans and the minority group of Reformed Protestants. The main effect was that the government of Prussia had full control over church affairs, with the king himself recognized as the leading bishop. In 1824 Frederick William III remarried (morganatically) Countess Auguste von Harrach, Princess of Liegnitz. They had no children. In 1838 the king distributed large parts of his farmland at Erdmannsdorf Estate to 422 Protestant refugees from the Austrian Zillertal, who built Tyrolean style farmhouses in the Silesian village.

Question: What is the religion of Frederick William IV of Prussia?
Answer: Prussian Union of churches.