Juan Fernández de Heredia (in Aragonese Johan Ferrández d'Heredia, pronounced Aragonese pronunciation: [ˈtʃwan feˈrand̪eθ deˈɾedʝa]; c. 1310 – 1396) was a Spanish knight of Aragon who served as Grand Master of the Knights Hospitaller from 24 September 1377 to his death. His tenure was occupied by the "affair of Achaea", the persistent, but ultimately fruitless, efforts by the Knights to acquire the Principality of Achaea in southern Greece. 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.