King John I of Portugal reigned from 1385 to 1433 and was a significant figure in the history of Portugal. He was the founder of the Aviz dynasty and played a crucial role in establishing Portugal's independence from Castile after the decisive victory at the Battle of Aljubarrota in 1385. John I is also known for his support of exploration and trade, which laid the groundwork for the Age of Discoveries. His marriage to Philippa of Lancaster strengthened ties with England, further enhancing Portugal's political and economic influence during his reign.