Duarte I was the King of Portugal from 1433 until his death in 1438. He was the son of King John I and Philippa of Lancaster, and he became king at a young age. His reign was marked by political instability and challenges, including conflicts with the nobility and issues related to governance. Despite these challenges, Duarte I is known for his contributions to literature and culture. He authored several works, including the "Livro da Ensinança de Bem Cavalgar" (Book on the Art of Good Horsemanship), which reflects his interest in chivalry and the ideals of knighthood.