Ferdinand I of Portugal
When King Ferdinand I of Portugal died in 1383, his only heir was Beatrice, married to king John I of Castile. In order to preserve Portuguese independence, the nobles supported the claim of King Ferdinand's half-brother John, Master of Aviz to the throne. After his first victory over the Castilians, in the Battle of Atoleiros (April 1384), John of Aviz named Nuno Álvares Pereira protector and constable of Portugal, in practice supreme commander of Portugal's armies, and count of Ourém. He was only 24 years old.