His father, both pre-occupied with his mistresses and out of favour with Friedrich II 'the Great', spent little time with his eldest son.
He received the usual military education, became a Lieutenant in 1784 and a Colonel in 1790. In 1793 he married the beautiful and very intelligent Luise of Mecklenburg-Strelitz; and in 1797, hesitant, good-looking and well-intentioned, he became king.
At once he tried to remedy his father's abuses, but did not have the ability to cope with the difficult foreign situation. For years Europe had been under the shadow of the French threat, so after a
while he chose the allied side against Napoleon. This led to the Prussian defeat at Jena in 1806 and Friedrich Wilhelm III and Luise were forced to flee to their ally, the Russian Emperor Alexander I.
The treaty of Tilsit, of 9 July 1807, gave most of Prussia's territory to France with what had been gained from Poland going to Russia. Queen Luise encouraged Gerhard von Scharnhorst, Karl von Clausewitz and August von Gneisenau in their military reform, but she died all too soon at only thirty-four years old.
Administrative reforms also took place, based on the French system. Feudal obligations, as far as they still existed, were eliminated and the status of serfdom abolished.
Friedrich Wilhelm III was forced to follow Napoleon in his Russian campaign but, everything went wrong for Napoleon, he changed sides to become the faithful follower of Alexander I. The Congres of Vienna gave Prussia areas of Pommern, Westphalia and Saxony. Reforms in both the army and administration continued despite Friedrich Wilhelm's opposition. Though Friedrich Wilhelm appeared to be a constitutional monarch, he distrusted all forms of Liberalism.
A religious man, he was well-meaning and tried to unite the Lutheran and Reformed Churches. But this took both coercion and confiscation to create an outward union based on common worship. He also came into conflict with the Roman Catholic Church over "mixed marriages". The revolutions in 1830 made Friedrich Wilhelm even more reactionary, but still his people loved him for his simplicity and the goodness of his heart.
Having been a widower for fourteen years, in 1824 he married Auguste von Harrach who was created F?rstin von Liegnitz as the marriage was regarded as morganatic. However, there were no children from this second marriage and, as her behaviour was irreproachable, the Royal family eventually approved of her.
 

Source: Leo van de Pas