Based on the moral ideas of the Cynics, Stoicism laid great emphasis on goodness and peace of mind gained from living a life of virtue in accordance with nature.

[14] Most of the details known about his life come from the biography and anecdotes preserved by Diogenes Laërtius in his Lives and Opinions of Eminent Philosophers written in the 3rd century AD, a few of which are confirmed by the Suda (a 10th-century Byzantine encyclopedia).

[15] Diogenes reports that Zeno's interest in philosophy began when "he consulted the oracle to know what he should do to attain the best life, and that the gods' response was that he should take on the complexion of the dead.

[17] Diogenes Laërtius describes Zeno as a haggard, dark-skinned person,[18] living a spare, ascetic life[19] despite his wealth.

From the day Zeno became Crates’ pupil, he showed a strong bent for philosophy, though with too much native modesty to assimilate Anaideia; Cynic “shamelessness” and the disregard for societal norms in favor of freedom.

An example of this may be found in the writings of Apuleius who narrates an incident where Crates and Hipparchia, his wife and fellow Cynic, engaged in a public act of sexual intercourse and, as such, drew a crowd.

Zeno, upon catching sight of this, covered them both with his cloak so as to prevent bystanders from witnessing the copulating couple, displaying his own inability to be apathetic to the expectations of society.

Apart from Crates, Zeno studied under the philosophers of the Megarian school, including Stilpo,[23] and the dialecticians Diodorus Cronus,[24] and Philo.

[27] Zeno began teaching in the colonnade in the Agora of Athens known as the Stoa Poikile (Greek Στοὰ Ποικίλη) in 301 BC.

His disciples were initially called "Zenonians," but eventually they came to be known as "Stoics," a name previously applied to poets who congregated in the Stoa Poikile.

Zeno is said to have declined an invitation to visit Antigonus in Macedonia, although their supposed correspondence preserved by Laërtius[29] is undoubtedly the invention of a later writer.

[34] We are also told that Zeno was of an earnest, gloomy disposition;[35] that he preferred the company of the few to the many;[36] that he was fond of burying himself in investigations;[37] and that he disliked verbose and elaborate speeches.

Striking the ground with his fist, he quoted the line from the Niobe: I come, I come, why dost thou call for me?and died on the spot through holding his breath.

Following the ideas of the Old Academy, Zeno divided philosophy into three parts: logic (a wide subject including rhetoric, grammar, and the theories of perception and thought); physics (not just science, but the divine nature of the universe as well); and ethics, the end goal of which was to achieve eudaimonia through the right way of living according to Nature.

[46] Zeno divided true conceptions into the comprehensible and the incomprehensible,[47] permitting for free-will the power of assent (sinkatathesis/συνκατάθεσις) in distinguishing between sense impressions.

But when he brought his left hand against his right, and with it took a firm and tight hold of his fist: – "Knowledge" – he said, was of that character; and that was what none but a wise person possessed.

[52] According to Zeno's beliefs, "[t]rue happiness" can only be found by obeying natural laws and living in tune with the course of fate.

[75] Zeno distinguished four negative emotions: desire, fear, pleasure and sorrow (epithumia, phobos, hêdonê, lupê / ἐπιθυμία, φόβος, ἡδονή, λύπη),[76] and he was probably responsible for distinguishing the three corresponding positive emotions: will, caution, and joy (boulêsis, eulabeia, chara / βούλησις, εὐλάβεια, χαρά), with no corresponding rational equivalent for pain.