High Quality Content by WIKIPEDIA articles Juan Fern ndez de Heredia (c. 1310 - 1396) was the Grand Master of the Knights Hospitaller from 24 September 1377 to his death. His tenure was occupied by the "affair of Achaea." He was also a great patron of the translation and composition of historiographical works in the Aragonese language and a counsellor to two Kings of Aragon.