Aesacus was the only(?) son of Priam, the last king of Troy, and Arisbe. Before his brother Paris was born, Aesacus interpreted a dream of Hecuba as meaning that Paris would one day destroy Troy. He urged them to expose the child, which they did.
Later, Aesacus saw and fell in love with Asterope, the daughter of a river god. When she saw Aesacus, Asterope fled into the forest. Aesacus pursued her, and Asterope was bitten by a snake. She died from the wound, and Aesacus was stricken with grief. He flung himself off a cliff into the sea. As he sunk into the sea, the Titan Tethys changed him into a bird and saved his life. Aesacus' heart was still broken, and so he tried again and again to drown himself in the sea, only to fail each time. Aesacus was changed into diver bird, plunging himself into the sea again and again only to return to its surface and an unwanted life.