Aegialeus was the elder son of Adrastus of Argos and a leader of the Epigoni who captured Thebes a generation after the Seven. He was the only Epigonus chief killed in that war — slain by Laodamas son of Eteocles at Glisas — and received heroic cult at Pagae in Megaris. He is distinct from Aegialeus the early king of Sicyon.
Adapted from Wikipedia, "Aegialeus (King of Argos)" · CC BY-SA 4.0
I.Son of Adrastus
Aegialeus is the son of Adrastus, leader of the Seven against Thebes, by Amphithea or Demonassa according to the handbook. While Adrastus was the only one of the Seven to survive the first war, his son belongs to the next generation that returns to finish it.
Through his sister Deipyle he is uncle to Diomedes; after Adrastus' death the Argive succession passes through that line and, in some accounts, through Aegialeus' own son Cyanippus.
II.Leader of the Epigoni
The Epigoni — sons of the Seven — march on Thebes and take the city. Aegialeus fights as one of their chiefs. At Glisas he is killed by Laodamas, son of Eteocles; sources disagree whether Laodamas then flees to the Encheleans (or Illyria) or is himself slain by Alcmaeon.
Handbooks underline the symmetry: Adrastus alone escaped the first war; Aegialeus alone of the Epigoni leaders falls in the second.
III.Cult and homonyms
Tradition held that Aegialeus' body was brought to Pagae in Megaris, where he received heroic worship; Adrastus is said to have died of grief afterward. Pausanias preserves the Pagae tomb notice.
A separate Aegialeus appears as an early Sicyonian king (sometimes identified with the land-name Aegialeia). The Epigonus is the Argive Adrastid; do not merge the two.