Usurper (lat. usurpare = to seize for use, to use) is a derogatory term used to describe either an illegitimate or controversial claimant to the throne in a monarchy, or a person who succeeds in establishing himself as a monarch without inheriting the throne, or any other person exercising authority unconstitutionally. It may also be applied to an official acting ultra vires, outside his authority or jurisdiction.

Some famous examples considered monarchical usurpers are Henry IV of England, Miguel of Portugal and Habibullah Ghazi of Afghanistan.

See also

• List of usurpers
• Pretender
• Roman usurper

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