In Greek mythology, Alcmaeon was son of the seer Amphiaraus and Eriphyle, leader of the Epigoni who took Thebes, and a matricide pursued by the Erinyes. After purification and wanderings he settled at the mouth of the Achelous; he was later murdered in Arcadia over the necklace and robe of Harmonia. His story filled lost epics and tragedies.
Adapted from Wikipedia, "Alcmaeon (mythology)" · CC BY-SA 4.0
I.Epigoni and matricide
Oracles and Pindar cast Alcmaeon as first through Thebes' gates among the Epigoni. Traditions differ on whether Eriphyle, bribed with Harmonia's robe, again forced a son to war, or whether Amphiaraus had already ordered vengeance. After the victory Alcmaeon killed his mother—sometimes with Amphilochus—for betraying Amphiaraus to the first Theban war.
The Erinyes drove him mad. He fled to Arcadia and then to King Phegeus of Psophis, who purified him and married him to Arsinoe (or Alphesiboea); Alcmaeon gave her the cursed necklace and robe.
II.Achelous, death, and variants
An oracle sent him to land that did not exist when he was polluted—the new silt of the Achelous—where he married the river-god's daughter Callirrhoe. When she demanded Harmonia's treasures, he fetched them under false pretences and was ambushed by Phegeus or his sons. Callirrhoe's sons Amphoterus and Acarnan later avenged him; Acarnania takes its name from that line.
Euripides' lost Alcmaeon in Corinth told another episode: children by Manto left at Corinth, a daughter sold into slavery, and an unwitting reunion. The epic Alcmeonis and several tragedies on Alcmaeon are known only by title or fragment.