Alcyoneus was in possession of the Isthmus of Corinth at the time when Heracles drove away the oxen of Geryon. The giant attacked him, crushed twelve waggons and twenty-four of the men of Heracles with a huge block of stone. Heracles himself warded off the stone with his club and slew Alcyoneus. The block with which the giant had attacked Heracles was shown on the isthmus down to a very late period. In another passage Pindar calls Alcyoneus a Thracian shepherd, and places the struggle with him in the Phlegraean plains.
His seven daughters are the Alkyonides.