14th century Byzantine Greek cleric and theologian
Source (Wikipedia): Gregory Palamas

Gregory Palamas was a Byzantine Greek theologian and Eastern Orthodox cleric of the late Byzantine period. A monk of Mount Athos and later archbishop of Thessalonica, he is famous for his defense of hesychast spirituality, the uncreated character of the light of the Transfiguration, and the distinction between God’s essence and energies. His teaching unfolded over the course of three major controversies, (1) with the Italo-Greek Barlaam between 1336 and 1341, (2) with the monk Gregory Akindynos between 1341 and 1347, and (3) with the philosopher Gregoras, from 1348 to 1355. His theological contributions are sometimes referred to as Palamism, and his followers as Palamites.