13th-century depiction of Muhammad ibn Zakariya al-Razi, published in "Recueil des traités de médecine" by Gerard of Cremona

Muhammad ibn Zakariya al-Razi was a Persian physician and chemist who, in the 9th century, was the first to document the distinction between the diseases of measles and smallpox.

Credit: Gerard of Cremona (c. 1250–60)