George Sphrantzes, also Phrantzes or Phrantza (Greek: Γεώργιος Σφραντζής or Φραντζής; 1401 – c. 1478) was a late Byzantine Greek historian and Imperial courtier. He was an attendant to Emperor Manuel II Palaiologos, protovestiarites ("Lord of the Imperial Wardrobe") under John VIII Palaiologos, and a close confident to Constantine XI Palaiologos. He was an eyewitness of the Fall of Constantinople in 1453, made a slave by the victorious Turks, but ransomed shortly afterwards. Sphrantzes served the surviving members of the Palaiologian family for the next several years until taking monastic vows in 1472. It was while a monk he wrote his history, which ends with the notice of Sultan Mehmed II's attempt to capture Naupaktos, which he dates to the summer of 1477; Sphrantzes is assumed to have died not long after that event.
He was born in Constantinople, during the Turkish blockade of that city; his godmother was the nun Thomais. In 1418 he was appointed attendant to Emperor Manuel. During his service to the Emperor Manuel, Sphrantzes did many favors for Constantine, developing a strong rapport with the future Emperor for, as he writes, "my uncle had been his tutor and my cousins and I were his companions, friends, and attendants." After the death of Manuel, he became the servant of Constantine and left with him 26 December 1427 when Constantine was appointed Despot of the Morea.
When they arrived in the Morea, Constantine made him governor of Glarentza, and Sphrantzes assisted Constantine in the latter's efforts to conquer the remainder of the Morea, but was captured 26 March 1429 in a skirmish outside of Patras and held prisoner until his relationship to Constantine was recognized, and he was paroled back to the Byzantine side to negotiate surrender of the citadel. While traveling to Epirus as an ambassador, to help arbitrate a peace between and his uncle's illegitimate sons over the succession to rule over Epirus, he was kidnapped by Catalan pirates, along with his retinue, and held at Cephalonia until the pirates took the group back to Glarentza where they were ransomed. Upon returning to Constantinople, he was made protovestiarites and appointed ambassador by the Emperor.