Agathon (c. 448-400 B.C) was an Athenian tragic poet and friend of Euripides and Plato. He is best known from his mention by Aristophanes (Thesmophoriazusae) and in Plato's Symposium, which describes the banquet given to celebrate his obtaining a prize for a tragedy (416). He probably died at the court of Archelaus, king of Macedonia. He introduced certain innovations, and Aristotle (Poetica, 9) tells us that the plot of his Antho was original, not, as usually, borrowed from mythological subjects.
See: Aristophanes, Thesmoph. 59, 106, Eccles. 100