Regent

16th century Swedish regent Stenonis Sture and wife Christina Gyllenstierna who both operated in strong resistance to Danish rule during the Kalmar Union
The oath of the provisional triumviral regents of the Empire of Brazil on behalf of the 5-year-old Emperor Pedro II in 1831, at the beginning of the Regency period.

In a monarchy, a regent (from Latin regens 'ruling, governing') is a person appointed to execute the office of a monarch temporarily, essentially as a substitute ruler. Regencies may arise for a number of reasons, including the monarch being a minor, ill, absent from the country, or otherwise unavailable. A regent may also be appointed in cases where the throne is vacant, or the identity of the legitimate monarch is disputed. The rule of a regent or regents is called a regency.