The protagonist Zadig is a smart, rich, moral young man who at the beginning of the novella feels assured of his future happiness. As a staunch rationalist, Zadig is not afraid to oppose the irrationality he sees in tradition and superstition, making himself a target for conservatives and fanatics. His intelligence both gets him into trouble and gets him out of it, but it does not make him happy. His mistaken belief that he can use his intelligence to control his emotions leads him to become a victim of them as he suffers a string of misfortunes.

Zadig is at turns naïve and cunning. He fails to anticipate the predictable consequences of his attempts at reform and remains oblivious to the role he plays in his fate. Yet, he is also a kind of trickster, using his cunning to expose people’s illusions and orchestrate events in his favor. Similarly, Zadig is at once selfless in his official duties as grand vizier of Babylon and self-centered in his outlook, aggrieved by his misfortune. These contradictions complicate his personality, lending it psychological realism.

While a Zoroastrian, Zadig opposes most theology and philosophy, considering them overcomplicated and fatuous.