Philippa of Lancaster was Queen of Portugal from 1387 until 1415 as the wife of King John I. Born into the royal family of England, her marriage secured the Treaty of Windsor and produced several children who became known as the "Illustrious Generation" in Portugal.

John I, also called John of Aviz, was King of Portugal from 1385 until his death in 1433. He is recognized chiefly for his role in Portugal's victory in a succession war with Castile, preserving his country's independence and establishing the Aviz dynasty on the Portuguese throne. His long reign of 48 years, the most extensive of all Portuguese monarchs, saw the beginning of Portugal's overseas expansion. John's well-remembered reign in his country earned him the epithet of Fond Memory ; he was also referred to as "the Good", sometimes "the Great", and more rarely, especially in Spain, as "the Bastard" (Bastardo).