Ferdinand I was King of Portugal for 16 years in the latter half of the 14th Century. Punctuating his reign were wars of succession in neighboring Castile.

He was born on Oct. 31, 1345, in Coimbra. His father was Prince Peter, oldest son and heir apparent to the reigning monarch, Afonso IV. His mother was Constanza Manuel.

Peter became king in 1357 and reigned for a decade. When he died, on Jan. 18, 1367, Ferdinand, his oldest son, became king.

Portugal and Castile had been allies and then antagonists, varying sometimes from year to year, from monarch to monarch. In 1369, Ferdinand made an attempt to take the throne of Castile. King Peter of Castile had died, at the hand of Henry of Trastamara, during a civil war. Ferdinand's grandfather had been the Castilian king Sancho IV, and so Ferdinand based his claim on that bloodline. Also claiming the throne were the kings of Aragon and Navarre and the Englishman John of Gaunt, whose wife, Constance, was the dead king's daughter.

The struggle devolved into one between Ferdinand and Henry, with the former giving up his claim in exchange for the hand of the latter's daughter, Leonora of Castile. Ferdinand, however, soon fell in love with another woman, with a similar name, Leonor Teles; it was this woman whom he married, in 1372.

John of Gaunt still wanted the Castilian throne and enlisted Ferdinand's help in pursuing it; as before, the fighting ended rather quickly in a treaty. When Henry died, in 1379, John of Gaunt and Ferdinand again allied. This time, however, as the conflict dragged on, Ferdinand decided that he had had enough and negotiated a separate peace with Castile, gaining an alliance in the form of a royal marriage, as his daughter Beatrice married John of Castile, Henry's son and successor.

Ferdinand and Leonor had no sons. When Ferdinand died, on Oct. 22, 1383, this lack of a male heir sparked a succession crisis. His brother, John, ultimately prevailed.