Abū Bakr Muḥammad ibn Zakariyyāʾ al-Rāzī, also known by his Latinized name Rhazes, 864 or 865 – 925 or 935 CE, was a Persian physician, philosopher and alchemist, widely considered one of the most important figures in the history of medicine. He also wrote on logic, astronomy and grammar.
A comprehensive thinker, al-Razi made fundamental and enduring contributions to various fields, which he recorded in over 200 manuscripts, and is particularly remembered for numerous advances in medicine through his observations and discoveries. An early proponent of experimental medicine, he became a successful doctor, and served as chief physician of Baghdad and Ray hospitals. As a teacher of medicine, he attracted students of all backgrounds and interests and was said to be compassionate and devoted to the service of his patients, whether rich or poor.
According to the Encyclopædia Britannica, he was among the first to use humoral theory to distinguish one contagious disease from another, and wrote a pioneering book about smallpox and measles providing clinical characterization of the diseases.