Frederick William , Elector of Brandenburg Frederick William ( ) ( 16 February 1620 – 29 April 1688 ) was Elector of Brandenburg and Duke of Prussia – and thus ruler of Brandenburg - Prussia – from 1640 until his death . A member of the House of Hohenzollern , he is popularly known as " The Great Elector " ( ) because of his military and political prowess . 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 - Westphalia political order of north - central Europe , setting Prussia up for elevation from duchy to kingdom , achieved under his son and successor . Biography . Elector Frederick William was born in Berlin to George William , Elector of Brandenburg , and Elisabeth Charlotte of the Palatinate . His inheritance consisted of the Margraviate of Brandenburg , the Duchy of Cleves , the County of Mark , and the Duchy of Prussia . Foreign diplomacy . During the Thirty Years ' War , George William strove to maintain , with a minimal army , a delicate balance between the Protestant and Catholic forces fighting throughout the Holy Roman Empire . Out of these unpromising beginnings Frederick William managed to rebuild his war - ravaged territories . In contrast to the religious disputes that distrupted the internal affairs of other European states , Brandenburg - Prussia benefited from the policy of religious tolerance adopted by Frederick William . With the help of French subsidies , he built up an army to defend the country . In the Second Northern War , he was forced to accept Swedish vassalage for the Duchy of Prussia according to the terms of the Treaty of Königsberg ( 1656 ) , but as the war progressed he succeeded in gaining full sovereignty for the Prussian duchy in the treaties of Labiau , Wehlau , Bromberg and Oliva , leaving the Holy Roman Emperor as his only liege for his imperial holdings . In the conflict for Pomerania inheritance , Frederick William had to accept two setbacks , one in the Northern War and one in the Scanian War . Though militarily successful in Swedish Pomerania , he had to bow to France ' s demands and return his gains to Sweden in the Treaty of Saint - Germain - en - Laye ( 1679 ) . Military career . Frederick William was a military commander of wide renown , and his standing army would later become the model for the Prussian Army . He is notable for his joint victory with Swedish forces at the Battle of Warsaw ( 1656 ) , which , according to Hajo Holborn , marked " the beginning of Prussian military history " , but the Swedes turned on him at the behest of King Louis XIV of France and invaded Brandenburg . After marching 250 kilometres in 15 days back to Brandenburg , he caught the Swedes by surprise and managed to defeat them on the field at the Battle of Fehrbellin , destroying the myth of Swedish military invincibility . He later destroyed another Swedish army that invaded the Duchy of Prussia during the Great Sleigh Drive in 1678 . He is noted for his use of broad directives and delegation of decision - making to his commanders , which would later become the basis for the German doctrine of Auftragstaktik , and he is noted for using rapid mobility to defeat his foes . Domestic policies . Frederick William is notable for raising an army of 40 , 000 soldiers by 1678 , through the General War Commissariat presided over by Joachim Friedrich von Blumenthal . He was an advocate of mercantilism , monopolies , subsidies , tariffs , and internal improvements . Following Louis XIV ' s revocation of the Edict of Nantes , Frederick William encouraged skilled French and Walloon Huguenots to emigrate to Brandenburg - Prussia with the Edict of Potsdam , bolstering the country ' s technical and industrial base . On Blumenthal ' s advice he agreed to exempt the nobility from taxes and in return they agreed to dissolve the Estates - General . He also simplified travel in Brandenburg and the Duchy of Prussia by connecting riverways with canals , a system that was expanded by later Prussian architects , such as Georg Steenke ; the system is still in use today . Marriages . On 7 December 1646 in The Hague , Frederick William entered into a marriage , proposed by Blumenthal as a partial solution to the Jülich - Berg question , with Luise Henriette of Nassau ( 1627 – 1667 ) , daughter of Frederick Henry of Orange - Nassau and Amalia of Solms - Braunfels and his 1st cousin once removed through William the Silent . Their children were as follows : On 13 June 1668 in Gröningen , Frederick William married Sophie Dorothea of Holstein - Sonderburg - Glücksburg , daughter of Philip , Duke of Schleswig - Holstein - Sonderburg - Glücksburg and Sophie Hedwig of Saxe - Lauenburg . Their children were the following :