Who founded Stoicism and who was its most important logician?

Stoicism was founded by Zeno of Citium in the early 3rd century BCE, who began teaching his philosophical system at the Stoa Poikile in Athens.12

The most important logician of the Stoic school was Chrysippus, who served as the third head of the school. Chrysippus was a prolific writer who systematized Stoic doctrine and made significant contributions to the history of logic, particularly through his development of propositional logic. Unlike the Aristotelian tradition, which focused on term logic, the Stoics under Chrysippus concentrated on inferences involving hypothetical propositions and established five basic, valid inference schemata known as indemonstrables.13245