George III was the grandson
of King George II
and at the age of 22 succeeded his grandfather
on the throne in 1760
. (George III's father Frederick had died already.) In 1761
he married Princess
Charlotte of Mecklenburg-Strelitz and the two had 15 children, 13 of whom survived to adulthood. The royal family had fairly simple tastes and lived in a more middle class
manner than had previous royalty, and George bought the building then called Buckingham House for the royal family to live in.
It was in 1764 that George first suffered an attack of an illness now believed to be porphyria. He recovered quickly this time, but asked Parliament to pass an act allowing him to appoint some other member of the royal family as regent for him if he fell ill for longer. This was a controversial piece of legislation but eventually did pass.
George was a more political king than some had been; he created the political party of "The King's Friends" to try and break the power of the Whig party. This eventually succeeded and the minster Lord North was appointed in 1770 to serve what the king wanted. George also was disappointed by the marriages of his brothers and got the Royal Marriages Act passed, which kept any descendant of George II (except for the families of princesses married into foreign royalty) from marrying under the age of 25 without the sovereign's consent, and over 25 from marrying if Parliament objected.
The American Revolution was a great blow to George, and in 1788 he had a second attack of illness, which lasted four months. After recovering, he dealt with the Napoleonic Wars on the European continent and the threat that Napoleon would invade England.
By 1805, his eyesight had started failing, and when his favorite daughter Amelia died in 1810, it seemed to trigger another attack of porphyria. On 11 February 1811, his son George IV was proclaimed Prince Regent, effectively reigning in the old king's place. (This is why the early part of the 19th century is known as the Regency era.) George III did not die until he was 81, in 1820, when George IV officially took the throne.