Nineteenth and early twentieth century scholars thought Cicero a bad source for Hellenistic philosophy. They thought that the speeches in his dialogues were translated, often badly, from single sources. Thus they read him only to reconstruct his sources by Quellenforschung. I first give a sympathetic account of these scholars’ projects, which is often dismissed too easily today. Second, I give a complete argument that these scholars were wrong, and that today’s more positive, but often incompletely defended, view of Cicero is correct. Third, I argue that Cicero wrote dialogues not only to introduce Hellenistic philosophy to a Latin audience, but also as literary unities to impress a learned Roman audience who already knew philosophy in Greek. His models for the dialogue form were Plato, Aristotle, and Heraclides of Pontus, but he adapted it to to serve his radical Academic skepticism, in which he followed Carneades and Clitomachus. He hoped to be the model for a Latin tradition of good writing about philosophy, that would "illuminate" both philosophy and Latin. Cicero’s creativity as a philosophical author shows why Quellenforschung failed, and that he is a good source for Hellenistic thought.