Galen: Greek physician and philosopher (born about 129 AD, died about 210 AD) known among other things for his discovery of blood in human arteries and for his dissection of the human cranial nerves, the nerves that supply key areas of the head, face, and upper chest.
The son of Nicon, a well-to-do architect and builder in Pergamum (Asia Minor), Galen had all the world open to him. He first studied philosophy, one of the traditional fields for a boy of his background. Nicon then had a dream in which Asclepius, the god of healing, told him to permit his son to study medicine. Galen began his medical studies in Pergamum at the age of 16-17. In search of medical knowledge, he then roamed about much of the eastern Mediterranean studying medicine in various cities including Smyrna (now Izmir, Turkey) and Corinth (Greece). He completed his studies at the famous medical school in Alexandria (Egypt). Galen returned to Pergamum and at age 28 was appointed physician to the school of gladiators, a post he occupied for four years and that some say made him "the first sports medicine specialist."
After that, a career in Rome was in the cards. There he went at age 32 and became a famous and influential physician, taking on cases that no one else could handle. The consultant's consultant, so to speak. He accompanied the Roman legions of Marcus Aurelius on their campaigns, and served as the personal physician to several emperors.
Galen performed surgical dismantling (dissection) of animals and humans and described what he saw (not always the practice of the day). He identified the majority (seven of the twelve) of the cranial nerves. He also did experiments such as severing a nerve and observing the effects. He is thus regarded as "the founder of experimental physiology."
Galen was the first to determine that arteries carried blood and not air! (For over 400 years the Alexandrian school of medicine had taught that arteries are full of air). Galen's theories about the blood circulation, however, were well off the mark and it was not until the 17th century that the great English physician William Harvey would challenge Galen's ideas in this regard.
With Hippocrates who preceded him by some 500 years, Galen was preeminent among the most distinguished physicians of antiquity. He knew all of the medical knowledge of his day, gathered it together, and wrote voluminously (and well) about it. Galen summed up the medicine of antiquity. His writing were a blessing to the ancient world. But they became a curse when, for more than a millennium, they were held to be the unassailable authority on medicine and this paralyzed the progress of medicine, something Galen would have greatly deplored.