A regent is a person who acts in place of a monarch while the monarch is too young to reign in his or her own right, or is incapacitated by illness, injury or captivity. It has also been the case that regents have served during an interregnum - that is, while a nation is formally a monarchy but no monarch has been appointed. This was the case in Hungary between 1919 and 1945, when the regent was Admiral Horthy; Finland was also officially ruled by a regent between 1917 and 1918, when it was established as a republic (this was probably the only case of an independent nation having a regent but never having a monarch).
The Prince of Wales, later the British king George IV, served for extended periods as regent during the later years of his father, George III, in the early nineteenth century. He was known as the Prince Regent, and this title gave its name to the Regency style of fashion, art, and, above all, architecture.