John Tzetzes (Greek: Ἰωάννης Τζέτζης) (c. 1110, Constantinople – 1180, Constantinople) was a Byzantine poet and grammarian, known to have lived at Constantinople during the 12th century. His most important work is the Chiliades.
Tzetzes was Greek on his fathers side and Iberian (Georgian) on his mother's side. In his works, Tzetzes states that his grandmother was a relative of the Georgian Bagratid princess Maria of Alania who came to Constantinople with her and later became the second wife of the sebastos Constantine Keroularios, megas droungarios and nephew of the patriarch Michael Keroularios.
Tzetzes was described as vain, seems to have resented any attempt at rivalry, and violently attacked his fellow grammarians. Owing to a lack of written material, he was obliged to trust to his memory; therefore caution has to be exercised in reading his work. However, he was learned, and made a great contribution to the furtherance of the study of ancient Greek literature.
The most important of his many works is considered to be the Book of Histories, usually called Chiliades ("thousands") from the arbitrary division by its first editor (N. Gerbel, 1546) into books each containing 1000 lines (it actually consists of 12,674 lines of political verse). It is a collection of literary, historical, theological, and antiquarian miscellanies, whose chief value consists in the fact that it to some extent makes up for the loss of works which were accessible to Tzetzes. The whole production suffers from an unnecessary display of learning, the total number of authors quoted being more than 400. The author subsequently brought out a revised edition with marginal notes in prose and verse (ed. T. Kiessling, 1826; on the sources see C. Harder, De J. T. historiarum fontibus quaestiones selectae, diss., Kiel, 1886).