Frederick William IV (German: Friedrich Wilhelm IV.), the eldest son and successor of Frederick William III of Prussia, reigned as King of Prussia from 1840 to 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, and in 1849 rejected the title of Emperor of the Germans offered by the Frankfurt Parliament as not the Parliament's to give.
A stroke in 1857 left the king partially paralyzed and largely mentally incapacitated, and his brother (and heir-presumptive) William served as regent from 1858 until the king's death in 1861, at which point the regent acceded to the throne as William I of Prussia.
Frederick William IV is buried with his wife in the crypt underneath the Church of Peace in the park of Sanssouci, at Potsdam.