Aelius Galenus or Claudius Galenus, often known as Galen or Galen of Pergamon, was a Roman Greek physician, surgeon, and philosopher who lived from September 129 to 216 AD. Galen, who is regarded as one of the most accomplished of all ancient medical experts, had an impact on the growth of several scientific fields, including anatomy, physiology, pathology, pharmacology, and neurology as well as philosophy and logic.

Galen acquired a thorough education that equipped him for a successful career as a physician and philosopher. He was the son of Aelius Nicon, a rich Greek architect with intellectual pursuits. Galen, who was raised in Rome, served prominent members of Roman society before being appointed as several emperors' personal physician. Galen was originally from the ancient city of Pergamon (modern-day Bergama, Turkey), and he travelled widely, becoming familiar with a wide range of medical theories and discoveries.
On the passions of the mind contains a description of Galen's early years. He was born in September in the year 129. His father, Aelius Nicon, was a well-to-do aristocrat who worked as an architect and builder and had a variety of hobbies, including literature, astronomy, mathematics, logic, and philosophy. As a "highly amiable, just, good and benevolent man," Galen characterises his father. At that time, Pergamon (modern-day Bergama, Turkey), a significant cultural and intellectual hub, was home to a sizable temple to the deity Asclepius as well as a library ranked second only to Alexandria's. Galen was introduced to both Stoic and Platonic thinkers in the city when he was just 14 years old.

Additionally, he studied the major philosophical schools of the day, such as Aristotelian and Epicurean. Galen's father carefully exposed him to literary and philosophical influences in preparation for a typical career in philosophy or politics. Galen claims, however, that his father had a dream in which the deity Asclepius arrived and gave Nicon the order to send his son to study medicine in the year 145.