Diogenes the Cynic, the ancient Greek who famously went around with a lamp in daylight, holding up to people's faces, looking for an honest person.

Wikipedia:
Diogenes the Dog

Many anecdotes of Diogenes refer to his dog-like behavior, and his praise of a dog's virtues. It is not known whether Diogenes was insulted with the epithet "doggish" and made a virtue of it, or whether he first took up the dog theme himself.

Diogenes believed human beings live artificially and hypocritically and would do well to study the dog. Besides performing natural bodily functions in public with ease, a dog will eat anything, and make no fuss about where to sleep. Dogs live in the present without anxiety, and have no use for the pretensions of abstract philosophy. In addition to these virtues, dogs are thought to know instinctively who is friend and who is foe. Unlike human beings who either dupe others or are duped, dogs will give an honest bark at the truth.

Diogenes stated that "other dogs bite their enemies, I bite my friends to save them."