John I of Portugal

John I, called John of Aviz (1357–1433), was the illegitimate son of Peter I of Portugal, made master of the Order of Aviz in 1364. When his half-brother Ferdinand I died in 1383 without a male heir, Beatrice's claim threatened Castilian annexation, triggering the 1383–1385 interregnum. John led the revolt, was acclaimed king at Coimbra in 1385, and won the Battle of Aljubarrota on 14 August 1385.

He founded the Aviz dynasty, married Philippa of Lancaster in 1387, and conquered Ceuta in 1415, beginning Portugal's overseas expansion.