Abū Bakr Muḥammad b. Zakariyyāʾ al-Razī, known in the Latin West as Rhazes, was a famed medical doctor and philosopher. Born in Rayy near modern-day Tehran in 251/865, he became familiar with the Arabic translations of Greek philosophical and medical texts at an early age. He followed the Galenic tradition in medicine, and headed the hospital in Rayy and in Baghdad. He was an extremely methodical and prolific scholar, his notebooks on medicine alone combined into twenty-five volumes, titled Kitāb al-Ḥāwī fī l-ṭibb, one of the most widely circulated and influential medical textbooks in Islamic history. His many works were registered in a bibliography by Bīrūnī, as well as in the Fihrist of Ibn al-Nadīm. He had a distinct approach to philosophy, differing from other well-known philosophers who followed the Aristotelian tradition, particularly with respect to his position on what he called Five Eternal Beings (al-qudamāʾ al-khamsa). Thus he was an original thinker with distinct positions on a number of important philosophical and medical issues, as well as being an expert doctor. Many of his works survive, yet have not been edited or published. Rāzī also worked and wrote on alchemy, and had important contributions to the field which influenced later alchemists. He died in 313/925.