The Reign of King João I: A Monarch of Resilience

King João I of Portugal (1357–1433)

Also known as John of Aviz, João I was born on April 11, 1357, in Lisbon. He ruled as King of Portugal from 1385 until his death on August 14, 1433, overseeing one of the most transformative periods in the nation's history. He is especially remembered for securing Portugal’s independence during a dynastic struggle with Castile and for founding the Aviz dynasty. His reign, lasting 48 years, remains one of the longest in Portuguese history and marked the dawn of Portugal’s Age of Exploration.

For his wise governance and enduring legacy, João I became affectionately known as “the Good” (o Bom) and “of Fond Memory” (de Boa Memória). Occasionally, especially in Spain, he was called “the Bastard”, a reference to his illegitimate birth.

Early Life and Rise to Power

João was the illegitimate son of King Pedro I of Portugal and a Galician noblewoman named Teresa, often identified as Teresa Lourenço. At the age of seven, in 1364, he was appointed Grand Master of the Order of Aviz, thanks to the influence of Nuno Freire de Andrade, the order’s Galician leader.

Following the death of his half-brother, King Ferdinand I, in 1383, Portugal faced a succession crisis. Ferdinand left no male heirs, and his only daughter, Beatrice, was married to John I of Castile. This raised fears that Portugal would fall under Castilian control, leading to widespread unrest and a period known as the 1383–1385 Interregnum, during which the Portuguese throne was effectively vacant.

On April 6, 1385, the Portuguese Cortes (royal council) convened in Coimbra and formally acclaimed João, then still Master of Aviz, as King of Portugal. This move sparked open conflict with Castile, which sought to enforce Beatrice’s claim.

Securing the Throne

Later that year, King John I of Castile invaded Portugal with French reinforcements. In response, João of Aviz—alongside his trusted commander Nuno Álvares Pereira—led Portuguese forces to a resounding victory at the Battle of Aljubarrota on August 14, 1385. The battle not only crushed the Castilian threat but also cemented João’s position as rightful monarch.

In the aftermath, Portuguese nobles who had supported Castile began defecting, surrendering towns and fortresses. João’s rule was now firmly established.

Alliance with England

On February 2, 1387, João I married Philippa of Lancaster, daughter of John of Gaunt, Duke of Lancaster. This union reinforced the longstanding Anglo-Portuguese Alliance, the oldest active alliance in the world today. Their marriage was also a cultural and intellectual partnership that produced a generation of influential royal children.

Peace and Expansion

With Castile no longer a threat, João was free to focus on strengthening the kingdom internally and exploring new frontiers. A significant turning point came in 1415, when Portuguese forces captured Ceuta on the North African coast. This strategic port opened the door to maritime trade in the Mediterranean and along the African coast. When Moroccan forces tried to retake Ceuta in 1419, they were repelled, affirming Portuguese control.

Seeking papal support for these military endeavors, João requested a declaration recognizing his campaigns as holy wars. In 1418, Pope Martin V issued a papal bull (Sane charissimus), which granted him religious legitimacy to conquer lands from Muslim rulers. This effectively allowed the enslavement of captives from these conquests, reflecting the era’s harsh realities.

Voyages of Discovery

Under the patronage of his son, Prince Henry the Navigator, João’s reign initiated Portugal’s exploratory efforts along the African coastline. These ventures led to the discovery of the Madeira Islands (1417) and the Azores (1427), both of which were soon colonized and claimed for Portugal. These efforts laid the groundwork for Portugal’s global maritime empire.

Character and Legacy

Contemporary accounts describe João as an intelligent, pragmatic, and thoughtful ruler. His early education in the religious Order of Aviz made him an unusually literate and cultured king for his time. He instilled a love of learning in his children, many of whom became prominent figures in European history.

This royal family came to be known in Portugal as the “Illustrious Generation” (Ínclita Geração):

Duarte (Edward), his successor, was a philosopher-king and writer.

Pedro, Duke of Coimbra, was a scholar and regent, known across Europe for his knowledge.

Henry the Navigator, Duke of Viseu, became the driving force behind early Portuguese exploration.

His daughter Isabella of Portugal married Philip the Good, Duke of Burgundy, becoming a patron of the arts and mother to Charles the Bold.

Conclusion

João I’s reign was a defining era for Portugal. From preserving national independence to igniting the first sparks of maritime empire, his leadership left a lasting imprint. His legacy is one of resilience, vision, and foundational change - a monarch who turned crisis into opportunity and set the stage for Portugal’s golden age.

Children

Blanche of Portugal (1388 - 1389) - Died in infancy.

Afonso of Portugal (1390 - 1390) - Died shortly after birth.

Duarte I (Edward I) of Portugal (1391 - 1438) - Succeeded João I as king. Father of Afonso V.

Pedro, Duke of Coimbra (1392 - 1449) - Regent for his nephew Afonso V.

Henry the Navigator (Infante Dom Henrique) (1394 - 1460).

Isabella of Portugal (1397 - 1471).

Ferdinand the Saint Prince (Infante Dom Fernando) (1402 - 1443)

Notable Illegitimate Children of João I and Inês Pires Esteves

Afonso, Duke of Braganza (1377 - 1461)

Infanta Beatriz of Portugal (1380 - 1439)

Inês was of non-noble background, reportedly the daughter of a Lisbon merchant or tradesman.

Some sources suggest she was of Jewish descent, which has been debated by historians but adds an interesting layer to his story, especially given how powerful Afonso and his descendants became.

To read further about the illigitimate children of the King and what became of them click here.