George III became King of Great Britain and Ireland on October 25, 1760, following the death of his grandfather, George II. His reign as king lasted for 59 years, making him one of the longest-reigning British monarchs. He was the third monarch from the House of Hanover and is perhaps best known for his role as King during the American Revolutionary War and for facing challenges such as the loss of the American colonies. George III's reign had a significant impact on British and world history.