Prince Regent (or Prince Regnant, as a direct borrowing from French language) is a prince who rules a country instead of a sovereign, e.g., due to the sovereign's incapacity (minority or illness) or absence (remoteness or non-existence).
Prince Regent in the UK
This title is normally associated with King George IV of the United Kingdom, who held it during the incapacity of his father, King George III (see Regent for other regents). Regent's Park and Regent Street in London are named after him.
This period is known as the English Regency, or just the Regency.
The title was conferred by the Regency Act on February 5, 1811. Subject to certain limitations for a period, the Prince Regent was able to exercise the full powers of the King. The precedent of the Regency crisis in the previous decade was followed, from which George III recovered before it was necessary to appoint a Regent. The Prince of Wales continued as regent until his father's death in 1820, when he became George IV.
Familiarly nicknamed "Prinny", George was unpouplar in many quarters, and was the subject of scurrilous cartoons in the press of the day relating to his various extravagances. An oft-reproduced cartoon by Gilray entitled A VOLUPTUARY under the horrors of Digestion shows a grossly fat Prince picking his teeth after an enormous meal. Behind him an overflowing chamber pot holds down lists of unpaid bills, while on a table against the wall stands a bottle labelled with a contemporary cure for the Pox.
Although other princes have served as regents (e.g. Prince Paul of Yugoslavia in the country from 1934 to 1941, Prince Luitpold and then Prince Ludwig of Bavaria from 1886 to 1913), they are not necessarily referred to as "the Prince-Regent."