The third chapter focuses on the Iranian doctor Abū Bakr al-Rāzī (sometimes called the 'Arab Galen'), who was attacked by later Islamicate thinkers for his disciplinary overreach, and his bid to replace Galenism with his more theologically informed system of medicine and philosophy. In particular, it argues that al-Rāzī seeks to weaken the epistemic authority of Galenism through his critiques of Galen’s explanations of certain ideas from Plato’s Timaeus. I first consider the Middle Platonic and Neoplatonic sources on which al-Rāzī may have drawn to elaborate his 'anti-Platonism' – his Platonism in response to Galen's Platonism. Turning finally to the Doubts about Galen, I demonstrate that al-Rāzī attacks Galen on the subjects of creation, pleasure, and the soul for neglecting God's role in the cosmos in his interpretations of the Timaeus. In reformulating the boundaries of medicine to include theological knowledge, which belonged in ancient epistemological schemes to metaphysics, al-Rāzī, I conclude, promotes the doctor-metaphysician in opposition to Galen’s more limited philosopher-doctor as the most reliable investigator of the cosmos.