He was born between 1388 and 1390 in Cañete, in what is now the province of Cuenca, as the illegitimate son of the Castilian noble don Álvaro Martínez de Luna, copero mayor (the page who poured drinks for a nobleman) of King Henry III of Castile, and María Fernández de Jarana, a woman of great character and beauty.

As the King was under pressure by greedy and unscrupulous nobles — among whom his cousins, the sons of Ferdinand, commonly known as the Infantes of Aragon, were perhaps the most dangerous — his reliance on a favourite who had every motive to be loyal to him, is quite understandable.

[5] Luna was also a master of all the accomplishments the King admired: a fine horseman, skillful with a lance and a writer of court verse.

The Encyclopædia Britannica Eleventh Edition recounts that to Juan de Mariana he appears as a mere self-seeking favourite.

In 1431, he endeavoured to employ the restless nobles in a campaign for the reconquest of Granada, the remaining territory of Muslim Spain and then ruled by the sultan Muhammed IX.

Luna, who had been Constable of Castile and Count of San Esteban de Gormaz since 1423, became Grand Master of the Order of Santiago by election of the Knights.

In 1453, the King succumbed to his wife's demands; Luna was arrested, tried and condemned to death, and soon executed by beheading at Valladolid on 2 June 1453.