King George III ( Born George William Frederick 4 June 1738 – 29 January 1820 ) was King of Great Britain and Ireland from 25 October 1760 until 1 January 1801 .
George III ( George William Frederick ; 4 June 1738 – 29 January 1820 ) was King of Great Britain and King of 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 in 1820 .