Frederick William I of Prussia (in German: Friedrich Wilhelm I), of the House of Hohenzollern (August 14, 1688 - May 31, 1740), often known as 'the Soldier-King', reigned as King of Prussia (1713 - 1740).

His father, Frederick I of Prussia, had successfully acquired the title King for the margraves of Brandenburg. Frederick William concentrated on building up the military power of Prussia.

During his reign, Frederick William I did much to centralize and improve Prussia. He replaced mandatory military service among the middle class with an annual tax, established primary schools, and resettled East Prussia (which had been devastated by the plague in 1709).

Frederick William was an extremely able administrator. He opposed all superfluous spending, so long as it did not concern his army. Frederick William paid the consumer tax he himself had imposed, and no candles were left burning at court. He lived frugally and worked hard and tirelessly for the welfare of his people. He encouraged farming, reclaimed marshes, stored grain in good times and sold it in bad times. He dictated the manual of Regulations for State Officials, containing 35 chapters and 297 paragraphs in which every public servant in Prussia could find his duties precisely set out. A minister or councillor failing to attend a committee meeting would lose six months' pay. If he absented himself a second time, he would be discharged from the Royal service.

In short, Frederick William was extremely concerned by every little aspect of his country so that it suited the needs of his army. His rule was absolutist and he was a firm autocrat. He practiced rigid economy, and at his death there was a large surplus in the treasury. The Prussian army was made an efficient instrument of war. Although Frederick William built up one of the most powerful armies in Europe and loved military pomp, he was essentially a peaceful man. He intervened briefly in the Great Northern War, but gained little territory.

Though he was peaceful, he was by no means gentle. His eldest surviving son was Fritz, born in 1712. Frederick William wanted him to become a fine soldier. As a little child Fritz was woken each morning by the firing of a cannon. At the age of 6 he was given his own regiment of children to drill as cadets and a year later he was given a miniature arsenal. Fritz was beaten for being thrown off a bolting horse and for wearing gloves in cold weather. Frederick William would frequently mistreat Fritz (he preferred his younger sibling August William), executing one of his closest friends, Hans Hermann von Katte, and almost disinheriting him.

Frederick William despised musicians, scientists and intellectuals, as well as all things French (in stunning contrast to his son Fritz). Fritz would become the greatest King of Prussia, Frederick II.

He acquired a reputation for his fondness for military display - leading to his special efforts to hire the tallest men he could find in all of Europe for a special regiment nicknamed Potsdam Giants.

Frederick William and his wife Sophia Dorothea of Hanover (daughter of King George I of Great Britain) had eight surviving children:

• Wilhelmine of Bayreuth (1709 - 1758)
• Friedrich II of Prussia (1712-1786)
• Friederike Luise (1714-1784)
• Philippine Charlotte (1716-1801)
• Sophie Dorothee Marie (1719-1765)
• Luise Ulrike of Sweden (1720-1782)
• August Wilhelm Prince of Prussia (1722-1758)
• Anna Amalia Princess of Prussia (1723-1787)
• Prinz Heinrich (1726-1802)
• August Ferdinand (1730-1813)