Portrait of Anthony I, King of Portugal and the Algarves (1531-95) wearing the medal of the Order of Aviz. The regal crown can be seen on the right hand side of the image. Two ships in a stormy sea are in the backgound.

Antonio was the illegitimate son of Prince Louis, Duke of Beja (1506–55). After the death of the old Cardinal-King Henry, the throne was disputed by several claimants including Philip II of Spain. Antonio, relying on the popular hostility to a Spanish ruler, presented himself as an alternative candidate.

He proclaimed himself King of Portugal in Santarém on 24 July 1580. However, he governed in the continent for only 20 days, culminating in his defeat in the Battle of Alcântara by the Spanish armies led by the Duke of Alba on 25 August. The throne of Portugal finally passed to King Philip II of Spain.