Diogenes of Sinope
The aim of Stoicism was to live a life of virtue, where "virtue consists in a will which is in agreement with Nature." As such, the sage is one who has attained such a state of being and whose life consequently becomes tranquil. The standard was so high that Stoics were unsure whether one had ever existed, if so, possibly only Socrates or Diogenes of Sinope had achieved such a state.