Democēdes in Harpers Dictionary of Classical Antiquities
（Δημοκήδης). A celebrated physician of Crotona (Herod.iii. 129). He practised medicine successively at Aegina, Athens, and Samos. He was taken prisoner by the Persians, in B.C. 522, and was sent to Susa to the court of Darius. Here he acquired great reputation by curing the king's foot and the breast of the queen Atossa. Notwithstanding his honours at the Persian court he was always desirous of returning to his native country, and in order to effect this, he procured by means of Atossa that he should be sent with some nobles to explore the coast of Greece and to ascertain in what parts it might be most successfully attacked. At Tarentum he escaped, and settled at Crotona, where he married the daughter of the famous wrestler Milo.
Democedes in Wikipedia
Democedes of Croton, described in The Histories of Herodotus as "the most skillful physician of his time".
Democedes was a Greek physician and a part of the court of Darius I. He was born in Croton, part of present-day Italy. His father was Calliphon, a priest as part of Asclepius. His first part as physician seems to be in civil service of Athens and Aegina. Later he entered service under Polycrates. In 522 B.C., Polycrates, his entourage, and Democedes were all captured as Lydians by Oroites and sent to Susa.
Herodotus describes the journeys of Democedes with much detail.
Darius and Atossa
Darius once sprained his ankle while he was hunting, and his Egyptian doctors could not help his ankle. This may seem a very small injury today, but medicine around those times was very primitive. However, Democedes was able to heal his ankle, and he was thereafter given great esteem. The court regarded his actions highly enough that he was able to eat in the presence of the emperor. He was the first of many Greek physicians to be within the Persian court. He lived in what the Persians regarded as luxury. Nevertheless, he always wanted to go back to his homeland, Greece. Later on, Darius's wife, Atossa, had a breast ulcer. When Democedes cured her ulcer, as a reward, he was set free and allowed to go to Greece, not necessarily stay.
He went to Greece as passenger on one ship of a reconnaissance mission for a later military campaign. Three Phoenician ships were sent with fifteen Persian nobles. Through the latter half of the mission, the fleet stopped in Tarentum, where Democedes made his escape with help from the Tarentian king. After his escape he went back to Croton. He was guarded from the Persians, and later married a daughter of Milon.