From the website of The National Cartoonists Society, http://reuben.org/ncs/members/biogs/berry.asp
The following information is excerpted from Encyclopaedia Romana, ©James Grout, 1997-2006:
Diogenes the Cynic
Diogenes of Sinope (fourth century BC) is too irascible a character not to share some anecdotes about him from the compendium of Diogenes Laertius on the lives of the philosophers... It was (his) determination to follow his own dictates and not adher to the conventions of society that he was given the epithet "dog," from which the name "cynic" is derived. Sold as a slave, he pointed and said, "Sell me to this man; he needs a master." The man heeded the advice, and entrusted Diogenes with his household and the education of his children.
Alexander the Great was reported to have said, "Had I not been Alexander, I should have liked to be Diogenes." Once, while Diogenes was sunning himself, Alexander came up to him and offered to grant him any request. "Stand out of my light," he replied. When asked why he went about with a lamp in broad daylight, Diogenes confessed, "I am looking for a [honest] man."...
... When invited to the house of Plato, he trampled upon his carpet, saying that he thereby trampled on the vanity of Plato, to which Plato retorted "How much pride you expose to view, Diogenes, by seeming not to be proud." To Plato's definition of a man as an animal, bipedal and featherless, Diogenes plucked a chicken and declared, "Here is Plato's man."
... When asked from where he came, Diogenes said, "I am a citizen of the world," and, when someone was queried as to what sort of man Diogenes was, the reply was given, "A Socrates gone mad."
In this detail from Diogenes (1882) by John William Waterhouse, the artist dutifully shows the lamp and the broken tub (and the diet of onions). But he also positions the philosopher next to a staircase, just as Raphael places him on the stairs in the The School of Athens. And the young woman substitutes for Alexander, standing between the sulking Diogenes and the sun. Too, she is painted to resemble the many terracotta figurines from Tanagra that had been discovered in the early 1870s in Boeotia and displayed in the British Museum... One sees, too, the influence of Alma-Tadema in the use of the staircase to compress movement downward and the figures in deep perspective.
References: Diogenes Laertius: Lives of the Eminent Philosophers (1925) translated by R. D. Hicks (Loeb Classical Library); Juvenal and Persius (1940) translated by G. G. Ramsay (Loeb Classical Library); J. W. Waterhouse (2002) by Peter Trippi.