George III was King of Great Britain and King of Ireland from 25 October 1760 until the union of these two countries on 1 January 1801, after which he was King of the United Kingdom of Great Britain and Ireland until his death. He was named after his father, and his father was named after his father, thus he was the third of his kind.
In the later part of his life, George III suffered from recurrent, and eventually permanent, mental illness.