In Greek mythology, Lycus was a ruler and regent of Thebes, brother of Nycteus, husband of Dirce, and uncle of Antiope. He persecuted Antiope until her sons Amphion and Zethus returned, killed or deposed him, and took the city. Parentage traditions vary (Spartos Chthonius; or Hyrieus and Clonia; or Poseidon and Celaeno). Distinct from other figures named Lycus.
Adapted from Wikipedia, "Lycus (son of Hyrieus)" · CC BY-SA 4.0
I.Regent and persecutor
Lycus and Nycteus flee Euboea after killing Phlegyas, settle at Hyria, then move to Thebes under friendship with Pentheus. After Polydorus and Labdacus, Nycteus and then Lycus hold the regency. When Antiope, pregnant by Zeus, flees to Epopeus of Sicyon, Lycus (on Nycteus's dying charge, or of his own will) fetches her back; she bears Amphion and Zethus on Cithaeron and the infants are left with shepherds.
In Thebes Dirce imprisons and tortures Antiope for years. The grown twins recognize their mother, march on the city, kill Lycus (or, in Euripides' Heracles tradition, are forbidden by Hermes to kill him but force the abdication), and bind Dirce to a bull. Laius, the rightful heir, is driven into exile.
II.Homonyms
The atlas id lycus is this Theban regent, not lycus-centaur, lycus-mariandyni, or other lesser Lycuses in the epic and local catalogues.