George III ( George William Frederick ; 4 June 1738 -- 29 January 1820 ) was King of Great Britain and Ireland from 25 October 1760 until the union of the two countries on 1 January 1801 , after which he was King of the United Kingdom of Great Britain and Ireland until his death . His life and with it his reign , which were longer than any other British monarch before him , were marked by a series of military conflicts involving his kingdoms , much of the rest of Europe , and places farther afield in Africa , the Americas and Asia . In the later part of his life , George III had recurrent , and eventually permanent , mental illness .
George III of the United Kingdom had experiences.