second son of King John I of Portugal, younger brother of King Edward, and uncle of Edward's son Afonso V, during whose minority he was regent.

The second of the “illustrious generation,” comprising the sons of John I and Philippa of Lancaster, Pedro was present at the conquest of Ceuta from the Muslims in 1415 and later traveled abroad in Europe, encouraging his younger brother Henry the Navigator in his discoveries. King Edward died young, leaving his foreign wife as regent for their young son Afonso V. Pedro successfully challenged her, took over the regency, married his daughter to the young King, and ruled the country until his illegitimate half brother, the head of the powerful Bragança family, mobilized opposition to him, obtained the young King's care, and forced Pedro into rebellion. He was slain at the Battle of Alfarrobeira.

His son Pedro the Constable, after a long exile in Castile, returned and was offered the crown of Aragon by a party in Barcelona, where he shortly died.