Dionysios the younger, on being banished a second time from Syracuse, went to Corinth and became schoolmaster. He is called Dionysios the tyrant. Hence Lord Byron says of Napoleon-
Corinth's pedagogue hath now Transferred his by-word to thy brow.
Ode to Napoleon, stanza xiv.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894