Duarte of Portugal (Edward, in English language), the Philosopher, eleventh king of Portugal, was born in Viseu in October 31 1391 and died in Tomar in September 13 1438. He was the son of John I of Portugal by his wife, Philippa of Lancaster. Duarte succeeded his father in 1433.

As a prince, Duarte always followed his father, king João I, in the affairs of the kingdom. He was knighted in 1415, after the capture of Ceuta. Duarte was made king in 1433 and soon showed interest in internal consensus. During is short reign of five years, Duarte called the Cortes (the national assembly) no less than five times to discuss internal affairs and politics. The king also followed the politics of his father concerning the maritime exploration of Africa. His brother, prince Henry the Navigator founded the navigation school of Sagres and Gil Eanes crossed the Bojador Cape during his reign.

In 1437, his brothers, princes Henry and Fernando persuaded Duarte to launch an attack on Morocco and thus win an African base for future Atlantic exploration. The expedition was not unanimously supported: princes Pedro, duke of Coimbra and João, duke of Aveiro were against the initiative and preferred to avoid conflict with the king of Morocco. They proved to be right. The resulting attack on Tangier was successful, but with great cost of men. Duarte's youngest brother prince Fernando was captured and eventually died in captivity. Duarte died of plague soon afterwards.

Another less political side of Duarte's personality is related with culture. A reflective and scholarly prince, he wrote the treatise O Leal Conselheiro (The Loyal Counsellor) as well as other books on hunting and several poems. Duarte was in the process of revising the Portuguese law code when he died.