Galen is the court physician of the Queen of Eddis. He is most likely based on Galen of Pargamum (A.D. 129-199/217), a promient Roman physician and philosopher of Greek origin, whose theories on anatomy and blood circulation influenced Western medical science for a milliennum.

Galen's appears only briefly at the end of The Thief, in order to tend to Eugenides's shoulder wound and fever. His primary appearence occurs in The Queen of Attolia, where he is the doctor who treats Eugenides after the amputation of his right hand. The Queen of Eddis recounts in The Queen of Attolia, that Galen was the one who treated Eugenides after violent encounters with his cousins and accidents he had as the Thief of Eddis. He does not accompany Eugenides to Attolia in The King of Attolia and Eugenides expresses gladness to leave "that torturing bastard Galen in the mountains." However, Galen does accompany Eddis to Attolia in A Conspiracy of Kings, where Eugenides is consternated by Galen competing with Attolia's own personal physician over the best way to maintain the king's health.

Galen frequently uses lethium as a sedative. As a physician, he has sworn an oath to Asklepious, who appears to be the Eddisian god of healing.