The first British-born monarch since Queen Anne, he was the second child of the Prince of Wales. He was educated by Lord Harcourt and the Bishop of Norwich. Only twelve years old, he lost his father and became his grandfather's heir, and king at twenty-two. His first love was Lady Sarah Lennox but, regarding her unsuitable, he decided on and married the German Princess Charlotte von Mecklenburg-Strelitz. She came to England and was crowned with him. They would become the parents of fifteen children. 
In 1764 the first attack of porphyria occurred. When he recovered he insisted on a law which would allow him to make Queen Charlotte, or any other member of the royal family, Regent in case the illness returned. The unsuitable marriages of two of his brothers led to the passage of the Royal Marriages Act in 1772. The American War of Independence distressed him greatly and, in 1789 porphyria returned more seriously to last for over three months. 
The French Revolution created even more concern and several attempts on his life were made. The last ten years of his reign involved England in the Napoleonic wars. His eyesight was failing and 
the death of his favourite daughter, Amelia, started the last attack of porphyria---and this time he never recovered. 
The Regency Act was passed and his eldest son, George (IV), became Regent for ten years. His last years were spent at Windsor, blind, deaf and mad. He was unaware of his wife's death though he himself did not die till two years later. 

Porphyria: a group of rare, inherited disorders caused by a flaw in 
the metabolism of porphyrins, the breakdown products of the red blood 
pigment. The condition may be in the liver (hepatic porphyria) or in 
the bone marrow (erythropoiryic porphyria) or both. Characteristic 
features of the defect are discoloration of the urine, which may turn 
dark brown if let standing for an hour or so; sensitivity to sunlight, 
which causes blistering skin rashes; bouts of abdominal pain; mental 
disturbances; and neuritis. 
The underlying genetic fault cannot be corrected, and there is no 
specific treatment.
 

Source: Leo van de Pas