Short answers, pulled from the story.
John Tzetzes was a Byzantine poet and grammarian who lived in Constantinople from around 1110 to 1180. He is important primarily because his major work, the Book of Histories, preserves fragments from more than 200 ancient Greek authors, including many whose original works have otherwise been lost.
The Book of Histories, also called the Chiliades, is a long poem of 12,674 lines of political verse divided into 660 topics. Each topic is a commentary on a learned reference from Tzetzes's own published letters. Its first editor, N. Gerbel, gave it the name Chiliades when he divided it into books of a thousand lines each in 1546.
The Chiliades preserves fragments from more than 200 ancient authors, including many whose works have been lost entirely. The work is considered an important source for knowledge that is unavailable anywhere else.
Tzetzes wrote several works engaging with Homer. The Antehomerica, Homerica, and Posthomerica together cover the events before, during, and between Homer's Iliad and Odyssey. He also wrote the Homeric Allegories, two didactic poems interpreting Homeric theology through euhemeristic, anagogic, and physical allegory, translated into English in 2015 and 2019 by Adam J. Goldwyn and Dimitra Kokkini.
Tzetzes described himself as pure Greek on his father's side and part Georgian on his mother's side. He recorded that his grandmother was a relative of the Georgian Bagratid princess Maria of Alania, and that she later became the second wife of Constantine Keroularios, the nephew of the patriarch Michael Keroularios.
Tzetzes wrote a commentary on the Alexandra, or Cassandra, a difficult poem by the Hellenistic poet Lycophron. Known as "On Lycophron," it was edited by K.O. Muller in 1811 and is considered the most important of Tzetzes's commentaries on individual Greek authors. His brother Isaac is generally associated with him in its production.