Nycteus (Ancient Greek: Νυκτεύς, "nocturnal") was a Theban king or regent whose rule followed Polydorus and passed to his brother Lycus. Father of Nycteis and Antiope, he dies — by suicide in Apollodorus, of battle wounds in Pausanias — after Antiope flees to Epopeus of Sicyon, charging Lycus to punish her. Through Nycteis he is grandfather of Labdacus in the Labdacid line.
Adapted from Wikipedia, "Nycteus" · CC BY-SA 4.0
I.Family
Nycteus and Lycus are sons of Chthonius one of the Spartoi, or of Hyrieus and the nymph Clonia (Hyrieus son of Poseidon and the Pleiad Alcyone), or of Poseidon and the Pleiad Celaeno. By Polyxo Nycteus has two daughters, Nycteis and Antiope. Nycteis marries Polydorus (Pentheus's successor) and bears Labdacus — linking the night-named house to the Labdacid stem. Keep `nycteus` distinct from his daughter `nycteis`.
II.Regency and death
The brothers flee Euboea after murdering King Phlegyas, settle at Hyria, then move to Thebes as friends of Pentheus. After Pentheus and Polydorus die, Nycteus becomes regent for the child Labdacus.
When Zeus impregnates Antiope and she flees to marry Epopeus at Sicyon, Apollodorus has Nycteus kill himself in shame after asking Lycus to punish her. Pausanias instead has him lead Thebans against Epopeus, take a mortal wound, and die at Thebes after charging Lycus to continue the war. Lycus then succeeds as regent.