The Persian physician of ninth- and tenth-century Rayy and Baghdad, Latinized as Rhazes, who ran hospitals, kept careful records of his patients, and wrote one of the earliest clear clinical accounts distinguishing smallpox from measles. His vast medical compendium, the Hawi or Continens, carried his case-based, observational style into the European universities, while his willingness to test Galen against his own findings made him one of the medieval world's sharpest clinical empiricists — and attacks on prophecy attributed to him by hostile opponents made him one of its most controversial figures.
When a patient came to him with fever and a rash, al-Razi did not reach first for a textbook. He watched. He noted the color of the eruption, the timing of the fever, the look of the patient's eyes, and he wrote it all down. Out of that habit came the first medical text that told smallpox and measles apart by their signs at the bedside, not by theory. He directed hospitals, kept running records of hard cases, and where his own eyes contradicted the great Greek authority Galen, he trusted his eyes. The Latin West knew him as Rhazes and studied him for centuries. His own world also remembered him as a man who, in works his enemies quoted back at him, questioned whether any prophet spoke for God.