King Cyzicus ruled over the Dolionians, a tribe that inhabited the southern shore of the Propontis. He gave his name to a city of the same name, Cyzicus, his capital.
King Cyzicus welcomed the Argonauts on their journey to Colchis; but after their departure, a storm drove them back to the Cyzicene coast at night. With neither the Argonauts nor King Cyzicus recognizing one another, each mistook the other as an enemy, and battle ensued. King Cyzicus was slain. The incident had been arranged by the gods Cybele, Pan (god) and Bellona (goddess) because Cybele wanted revenge against Cyzicus for killing one of her lions. When day broke, the Argonauts realized their tragic mistake, and granted Cyzicus an elaborate burial.
King Cyzicus left behind a young bride named Cleite, daughter of Merops of Percote. Cyzicus's parentage is given as Aeneus by Aenete (or Aenippe), daughter of Eussorus; or else Eussorus is given as his father. King Cyzicus is sometimes referred to as a Thessalian migrant (hence his hospitality to the Argonauts, many of whom hailed from Thessaly, including Jason himself). The name Aeneus recalls the Thracian city of Aenus, although Aeneus is said to be the son of Apollo and Stilbe, a daughter of the Thessalian River Peneus.