Abu Bakr Muhammad ibn Zakariya Razi (Rhazes) was an Iranian physician, chemist, philosopher and scholar who lived from 865 to 925 (Fig. 1). Rhazes was born in Ray outside Tehran, Iran [1]. He studied medicine in his 30s or 40s and completed his medical training in Muqtadiri Hospital (the main hospital of Baghdad), mainly under Ali Ibn Rabane. After finishing his training, Rhazes left Baghdad for Ray, his native city, to take charge of the local hospital, where he gained eminence as a clinician. Because of his reputation, the Caliph in Baghdad appointed him the head of themain hospital in Baghdad and a court physician in 907. He traveled widely, visiting famous medical centers of his time in Jerusalem, Cairo, and Cordova. Aftermany years in Baghdad, he returned to Ray, where he died in 925 [1,2]. Rhazes is considered one of the two greatest physicians in medieval medicine. While the other, Avicenna (937 to 1037), contributed to the theory of medicine, Rhazes contributed to the practice of medicine. He is regarded as one of the most original of the Iranian writers who followed both Hippocrates and Galen in their methods and their ideas. Rhazes combined knowledge of textual scholarship with astute clinical observation [2,3]. As chief physician of the Baghdad hospital, Rhazes formulated the first known description of smallpox [4]. Rhazes is also known for having discovered allergic asthma, and was the first physician ever to write articles on allergy and immunology [5,6]. Rhazes left more than 200 treatises on various subjects. The most well known is Kitab Al Hawi Fi Al-Tibb, also known as Liber Continens, a 25-volume medical encyclopedia. Here he translated some works of Greek physicians and addedmaterial from other Greek aswell as Indian and Arabic authors, interspersing this with knowledge from his own experience [2–7]. In his book “Doubts about Galen (Shukuk 'ala alinusor)”, Rhazes rejects several claims made by the Greek physician, as far as the alleged superiority of the Greek language and many of his cosmological and medical views. He links medicine with philosophy, and states that sound practice demands independent thinking [2,7,8]. Medical practice by Rhazes in the 9th and early 10th centuries inspires us with the fact that he had understanding of evidence-based decision making. Rhazes believed that contemporary scientists and scholars are by far better equipped, more knowledgeable, and more competent than the ancient ones, due to the accumulated knowledge at their disposal. His attempt to overthrow blind acceptance of the unchallenged authority of ancient sages, encouraged and stimulated research and advances in the arts, technology, and sciences. Despite the fact that he was a Galenist in his theories, he followed the principles of Hippocrates in observing his patients, taking a detailed medical history and writing keen notes [2]. Rhazes rejected several claims made by Greek physicians regarding the alleged superiority of Greek language and medicine. Although an avid follower of Galenic thought, Rhazes rejected many teachings of Galen in his book Shukuk book “Doubts About Galen (Shukuk 'ala alinusor)” [2,5,7]. Rhazes disagreed that the brain, spinal cord, and ventricles were formed in pairs. He also disagreed with Galen who did not relate hemiplegia to hemisphere involvement but rather to ventricular involvement [7]. In some cases he was correct, as when he concluded that copious urine formation in the winter was due to less perspiration, rather than to excess sediments as the Greeks believed. He was sometimes wrong