Zeno of Citium (c. 334–262 BCE) was a Hellenistic philosopher and the founder of the Stoic school in Athens. Born in Cyprus, he moved to Athens as a young man and studied under various teachers, including Cynic and Academic philosophers. He began teaching in a public colonnade called the Stoa Poikile, which gave his followers the name "Stoics." His philosophy presented a unified system of logic, physics, and ethics, arguing that virtue—achieved by living in accordance with nature and reason—was the key to a good life. He was highly respected in Athens and died there in old age.

While Zeno wrote several works, none survive in complete form. Among his lost writings is a collection of letters. These letters survive only as fragments and references in the works of later authors. The exact number and full content of these letters are unknown, and modern scholars note that the authenticity of all material attributed to him is difficult to confirm.

Zeno’s historical importance is foundational. As the founder of Stoicism, he established a philosophical tradition that would become one of the most influential in the ancient world. His core ideas were developed by his successors and profoundly shaped Greco-Roman thought for centuries, directly influencing later Roman Stoics like Seneca, Epictetus, and Marcus Aurelius. The fragments of his letters, though scant, are part of the early evidence for his teachings and the practice of philosophical correspondence.