George Hamartolos or Hamartolus (Greek: Γεώργιος Ἁμαρτωλός) was a monk at Constantinople under Michael III (842–867) and the author of a chronicle of some importance. Hamartolus is not his name but the epithet he gives to himself in the title of his work: "A compendious chronicle from various chroniclers and interpreters, gathered together and arranged by George, a sinner (ὐπὸ Γεωργίου ἁμαρτωλοῦ)". It is a common form among Byzantine monks. Krumbacher (Byz. Litt., 358) protests against the use of this epithet as a name and proposes (and uses) the form Georgios Monachos (Γεώργιος Μοναχός "George the Monk").
Nothing is known about him except from the internal evidence of his work, which establishes his period (in the preface he speaks of Michael III as the reigning emperor) and his calling (he refers to himself several times as a monk).
The chronicle consists of four books. The first treats of profane history from Adam to Alexander the Great; the second, of the history of the Old Testament; the third, of Roman history from Julius Caesar to Constantine; and the fourth down to the author's own time, to the death of the emperor Theophilus (842), whose widow Theodora restored the veneration of icons in the same year. The chronicle is the only original contemporary authority for the years 813–842, and therefore so far indispensable. As usually in the case of such medieval chronicles, the only part to be taken seriously is the account of more or less contemporary events. The rest is interesting as an example of Byzantine ideas on the subjects, and of the questions that most interested Byzantine monks.