His youth was overshadowed by his father suffering from porphyria, bringing first fear for his father's outbursts but later, with his favourite sister Wilhelmine, they would tease him. However, he was sadistically treated and humiliated in public because his father disapproved of his playing the flute and did not appear to be the soldier his father wanted him to be.
At the age of eighteen he failed when trying to flee his father's territories accompanied by his friend Lieutenant von Katte. They were caught and Friedrich was forced to watch Katte's execution. For a period Friedrich was kept imprisoned and, in 1733, had to accept Princess Elisabeth Christine of Brunswick-Wolfenbuettel as his bride.
In 1740 he succeeded his father and it was expected that he would indulge in his artistic pursuits and leave the governing to his ministers. The territories to which Friedrich II succeeded were two
large areas, the March of Brandenburg and East Prussia, as well as many small areas scattered in the west of Germany. He also inherited a splendid army and, within four months of his accession, he bullied an aged bishop into paying a huge indemnity. A small incident, but it made Europe's rulers pay attention to this young newcomer on Europe's stage.
Before his first year was over he invaded Silesia, one of Austria's richest provinces, to a small part of which he had a flimsy claim. However, expecting only token opposition from the inexperienced
Empress Maria Theresa, he took the whole area. Although the Austrians sent an army, they were defeated and four years of sporadic warfare followed. Friedrich emerged as a great military commander but with Maria Theresa as his arch-enemy. Three times he allied himself with France but breaking these alliances whenever it suited him. He kept Silesia, increasing his territories by a third.
In his rule he was despotic but also surprisingly human and enlightened. His days usually began with flute playing and ended with a concert, but in the hours between he worked hard for his people. He improved the legal system, abolished torture except for high treason, and introduced religious tolerance. He was his own minister of finance and trade and supervised agriculture and industry. All his subjects had access to him, at least in writing.
In 1745 Voltaire called him "the Great" but it was his actions in the Seven Years' War which really earned him the title. France, Austria and Russia united with Prussia's destruction in mind. Seven
years of bitter warfare followed and Prussia was faced with certain defeat. However, the death of Russia's Empress, followed by the succession of Friedrich's admirer, Peter III, halted Russia's
involvement in the war. Then, with support of the English, the French were defeated and finally the Austrians. The peace treaty of 1763 left his country intact as well as in possession of Silesia.

Energetically he reconstructed his country and, when he died, he left Prussia more prosperous than it had been before the start of the Seven Years' War. Also, 'Old Fritz' became a cult figure, around which later German nationalist feelings would concentrate.
 

Source: Leo van de Pas