He was owned by the three-headed Titan, Geryon. Orthrus and his master, Eurytion, were charged with guarding Geryon's herd of red cattle in the "sunset" land of Erytheia ("red one"), one of the islands of the Hesperides in the far west of the Mediterranean. Heracles eventually slew Orthrus, Eurytion, and Geryon, before taking the red cattle to complete his tenth labor.
Orthrus was one among Echidna's fearsome brood listed in Hesiod, Theogony (306ff). According to some sources, it was he rather than Typhon sired with her further chthonic monstrous creatures: the Chimera, the Sphinx (Iliad ix.664), the Lernaean Hydra, and even, Hesiod says, the Nemean lion.
In one story, Orthos was captured and tamed by Oedipus.