Nikephoros Gregoras, Latinized as Nicephorus Gregoras, Byzantine astronomer, historian, man of learning and religious controversialist, was born at Heraclea Pontica.
At an early age he settled at Constantinople, where his reputation for learning brought him under the notice of Andronicus II Palaeologus, by whom he was appointed chartophylax. In 1326 Gregoras proposed certain reforms in the calendar, which the emperor refused to carry out for fear of disturbances; nearly two hundred years later they were introduced by Gregory XIII on almost the same lines.
When Andronicus was dethroned by his grandson Andronicus III Palaeologus, Gregoras shared his downfall and retired into private life. Attacked by Barlaam, the famous monk of Calabria, he was with difficulty persuaded to come forward and meet him in a war of words, in which Barlaam was worsted. This greatly enhanced his reputation and brought him a large number of pupils.
Gregoras remained loyal to the elder Andronicus to the last, but after his death he succeeded in gaining the favour of his grandson, by whom he was appointed to conduct the unsuccessful negotiations with the ambassadors of Pope John XXII. Gregoras subsequently took an important part in the Hesychast controversy, in which he violently opposed Gregorius Palamas, the chief supporter of the doctrine. After the doctrines of Palamas had been recognized at the synod of 1351, Gregoras, who refused to acquiesce, was practically imprisoned in a monastery for two years. Nothing is known of the end of his life.