Diogenes by: John William Waterhouse (1882), Salvator Rosa (1650s), Jean-Léon Gérôme (1860) and Jules Bastien-Lepage (1873)
Diogenes (c.412-323 BC) was a Greek philosopher from Sinope (in modern-day Turkey). To describe Diogenes as a controversial character would be a bit of an understatement; he managed to get himself banished from Sinope for defacing coins, he then continuously criticised Athenian society whilst living there, calling it corrupt and sinful, and he publicly humiliated both Plato and Alexander the Great.
Little is known about the teachings of Diogenes, as none of his writings have survived. However, from various written accounts, he has been identified as having Stoic beliefs in the importance of action over though or speech in communicating a virtuous life.
'I am not an Athenian or a Corinthian, but a citizen of the world.' - Diogenes of Sinope