Galen (Galenus), Claudius, an ancient physician, born in Pergamus in Mysia, A. D. 130, died, according to Suidas, in 200 or 201, but according to his Arabic and some other biographers, from 10 to 18 years later. Galen at 15 studied logic and philosophy; two years afterward he began the study of medicine; and at about the age of 20 he travelled into various countries to complete his education. He was absent from Pergamus nine years, and when he returned he was appointed city physician to the school of gladiators. Some popular commotions having arisen a few years after his appointment, he went to Pome, where he spent about four years, and acquired great reputation for skill in anatomy and medicine. As soon as the troubles in Pergamus had passed away, Galen hastened back; but hardly had he reached his destination when he was summoned by the emperors Marcus Aurelius and Verus to attend them at Aquileia where a pestilence raged in the camp. Verus died of apoplexy on the way to Pome, and Galen accompanied Marcus Aurelius thither. When returning to the camp after the apotheosis of his colleague, Marcus Aurelius urged Galen to accompany him, but he declined under pretence that Aesculapius had enjoined him to remain.

How long he sojourned in Pome during his second visit is uncertain, but while there he continually added to his fame by his lectures, writings, and practice. He ultimately returned to his native city, and died there. Galen was not only the most eminent physician, but also one of the most learned and accomplished men of his age; and for more than 1,000 years after his death his authority in medical matters was regarded in Europe as almost supreme. He was a very voluminous writer on medical and philosophical subjects. There are still extant 83 treatises of his, and 15 of his commentaries on various works of Hippocrates, besides fragments of his lost works and writings falsely attributed to him. The best edition of his works is that by Kuhn (20 vols. 8vo, Leipsic, 1821-'33). Writings attributed to him were discovered and published in Paris by Minas in 1844, and by Daremberg in 1848.