During research seminars, it hardly ever happened that Gerard Debreu posed a question—and if he did, not without already knowing the answer. While some admired him for the tranquility of his austere rigor, others wondered how little he had to say in economics. To whatever effect, Debreu himself was committed to mathematics since he could earn recognition without exposing himself as a person. This essay presents his life and career in light of this personal need for protection by mathematical purity. My account profited from Debreu‘s personal papers as well as the memories of former colleagues, friends, and family who communicated more freely about Debreu than he himself ever could.