Dercynus

In Greek mythology, Dercynus (Ancient Greek: Δέρκυνος) was a son of Poseidon and brother of Alebion (Ialebion). The two brothers engaged into battle with Heracles at Liguria of North-Western Italy. This version was mentioned in Aeschylus' play Promētheus Lyomenos, now lost. In some sources, Dercynus was named as Ligys  and Bergion (Βεργίων) or Beergios.

Mythology
Having obtained the Cattle of Geryon as his tenth labour, Heracles was passing through Liguria, on his way back to Mycenae from Iberia. Dercynus and Albion were supported by a numerous army. The battle that followed was fierce. Hercules and his army were in a difficult position so he prayed to his father Zeus for help. With the aegis of Zeus, Heracles won the battle and both brothers were killed. It was this kneeling position of Heracles when prayed to his father Zeus that gave the name Engonasin ("Εγγόνασιν", derived from "εν γόνασιν"), meaning "on his knees" or "the Kneeler" to Hercules' constellation. The story is also alluded to in Hyginus, Dionysius and Strabo.