In Greek mythology, Oeagrus (Ancient Greek: Οἴαγρος; Greek: Οίαγρος), son of Pierus or Tharops, was a king of Thrace. He and the muse Calliope were the parents of Orpheus and Linus. He was also sometimes called the father of Marsyas. There are various versions as to where Oeagrus's domain was actually situated. In one version, he ruled over the Edonian kingdom in the region of Mygdonia. He is also connected with Pieria, further west, or to the vicinity of the River Hebrus to the east; the latter was said to be called 'Oeagria', in his honor.

Not surprisingly, the parentage given for Oeagrus also differs between accounts. In the version that places Oeagrus in Pieria, his father is given as King Pierus and Methone. In the version that places him in Edonia he is said to be the son of Charops, an adherent of the god Dionysus; Charops was invited by Dionysus to rule over the Edones after the violent death of their king Lycurgus. Oeagrus has also sometimes been called the son of the god Ares, who was associated with Thrace.

Oeagrus is given as the father of Orpheus with mother Calliope (sometimes Apollo is given as the father), and he is described as "a Thracian wine-god, who was himself descended from Atlas." He married Calliope close to Pimpleia, Olympus.