Like Cleon, he counts as a demagogue, one who exercised power solely through speech in the assembly. He is universally reviled in the sources, even more so than his predecessor: both are associated with an alleged decline in Athenian political culture leading to the loss of the war with Sparta. Thucydides 8.73 is particularly vicious. In attacks on him in comedy he is represented as being of slavish and foreign background, both of which are improbable. But unlike Pericles (a demagogue in fact himself) he did not have a noble background.
The legislation that survives under his name tells a somewhat different story.
Somewhere in the years 417-415 BC he was ostracised, perhaps the last person to be subject to the practice. Accounts of this ostracism in Plutarch descibe a complex struggle with Nicias and Alcibiades, where Hyperbolos tried to bring about the ostracism of one of this pair but they combined their influence to induce the people to expel Hperbolos instead. The validity of Plutarch's take on these events, however, is hard to gage.
Hyperbolos went to live on the island of Samos where he was murdered in 411 BC by right-wing revolutionaries around the time of the oligarchic coup of the 400 that for several months suppressed the democracy at Athens.
Oxford Classical Dictionary, 2nd edition (Oxford 1996): Hyperbolus
'The Ostracism of Hyberbolus', J.P. Rhodes, in Ritual, Finance, Politics: Athenian Democratic Accounts presented to David Lewis, edd. R. Osborne, S. Hornblower (Oxford 1994), p. 85-99
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