This article will focus on Cicero’s ethics and the way he inherits some stoic concepts to build his own philosophical view about “what to do”. It is well known that Cicero’s De Officiis is based on Panaetius’s Peri kathekontos, as far as the structure of the book is concerned. It is far more difficult to depart exactly what he owes to Stoics (Panaetius and others, like Hecato and Posidonius) and what he builds. The aim is finally to shed some light on Cicero’s conceptual inventivity, especially when duty (officium, kathekon) and moral character (persona, prosôpon) are concerned. It will enable us to understand the possible role played by Cicero in the building of a very important notion for modern ethics: the paradigm of the vir bonus, which will become the paradigm of the Gentleman later on.