old Brutus Lucius Junius Brutus was considered to be the founder of the Roman Republic. In 509 BC he inspired the Romans to expel the last king, Tarquin the Proud, and his kin. The immediate cause of his rebellion against Tarquin was the rape of Lucretia, the wife of a friend, by Sextus, one of Tarquin's sons. Shakespeare told Lucretia's story in his narrative poem, The Rape of Lucrece, in which Lucius Junius Brutus says of Sextus' abominations, "Rome herself in them doth stand disgraced."

Marcus Brutus thought Lucius Junius Brutus was an ancestor of his, but there are more than 400 years between the two men, and the "Brutus" in "Lucius Junius Brutus" is a cognomen, which reflects the fact that Lucius Junius as a young man pretended to be a dullard and a fool (a "brute") in order to escape the fate of many of his kin, who had been murdered on the order of Tarquin.