Diogenes (412-323)

Diogenes the Cynic, also known as Diogenes of Sinope, was an ancient Greek philosopher during the period of Classical Greece, and one of the founders of Cynicism.

Quotes

As a matter of self-preservation, a man needs good friends or ardent enemies, for the former instruct him and the latter take him to task.
When two friends part they should lock up each other's secrets and exchange keys. The truly noble mind has no resentments.
Discourse on virtue and they pass by in droves. Whistle and dance the shimmy, and you've got an audience.