In Greek mythology, Medus (also Medeus or Medeius) was the son of Medea — by Aegeus in the Athenian strand, or by Jason in Hesiod and related notices — and the eponym of the Medes / Media. Driven from Athens with his mother after the plot against Theseus, he later kills Perses of Colchis (or helps restore Aeëtes) and conquers land named for himself or Medea. Distinct from other Media-etymologies that credit Medea alone.
Adapted from Wikipedia, "Medus" · CC BY-SA 4.0
I.Parentage
Apollodorus, Hyginus, and others make Medus son of Aegeus and Medea, half-brother of Theseus. Hesiod's Theogony and Pausanias (citing Hellanicus) instead give Jason as father; in that strand Medeus is raised by Chiron. Some call him Polyxenus and give him a sister Eriopis.
When Medea's plot against Theseus fails, mother and son flee Athens.
II.Colchis and Media
Hyginus has Medus storm-driven to Perses, brother of Aeëtes and usurper of Colchis. Captured, he claims to be Hippotes son of Creon. Medea arrives posing as a priestess of Artemis, nearly has the "Corinthian" sacrificed, then recognizes her son, arms him, and has him kill Perses and reclaim the kingdom — or she stabs Perses herself; other tellings restore Aeëtes.
As king Medus campaigns above the Pontus and names the land Media; Hyginus also credits him with founding Meda in Ecbatana. Apollodorus has him die marching against the Indians.