Diogenes - "The Cynic"
Diogenes was chief among the school known as the cynics, though possibly not representative of it [Diogenes "carried the principles of the sect to an extreme of asceticism." (OED.)]. It was said of Diogenes that throughout his life he "searched with a lantern in the daylight for an honest man." And though Diogenes apparently did not find an honest man, he had, in the process, "exposed the vanity and selfishness of man." (Chambers.)
The sect, known as the cynics, was founded by Antisthenes (444-370 BC), a pupil of Socrates; it was "marked by an ostentatious contempt for ease, wealth, and the enjoyments of life." Diogenes was a pupil of Antisthenes. Diogenes, on coming to Athens from his native lands, Sinope, came as "a rake and spendthrift." After following under the spell of Antisthenes, Diogenes "became at once an austere ascetic, his clothing of the coarsest, his food the plainest, and his bed the bare ground. At length he found himself a permanent residence in a tub."
(The meaning of cynicism today is to be found in the OED. "A person disposed to rail or find fault; now usually: One who shows a disposition to disbelieve in the sincerity or goodness of human motives and actions, and is wont to express this by sneers and sarcasms; a sneering fault-finder." The image of a cynic that has come to us is that of a dog.)
An interesting story is the one where the young Alexander the Great (356-323 BC) met Diogenes, then a very old man. The powerful young conqueror, being solicitous of the old philosopher, asked what, if anything he could do for him. Diogenes replied, "Stand out of my sunshine"; to which he added, as Alexander took his leave, "If I were not Alexander, I would be Diogenes."