By giving shelter to the fugitive Eadgils, a rebel against his uncle the king of the " Swain " (the Swedes, dwelling to the north of the Gautar), Heardred brought on himself an invasion, in which he lost his life.
When Beowulf became king, he supported the cause of Eadgils by force of arms; the king of the Swedes was killed, and his nephew placed on the throne.
The Swedish princes Eadgils, son of Ohthere, and Onela, who are mentioned in Beowulf, are in the Icelandic Heimskringla called Adils son of Ottarr, and Ali; the correspondence of the names, according to the phonetic laws of Old English and Old Norse, being strictly normal.
In each, a hero from Gautland slays a destructive monster at the court of a Danish king, and afterwards is found fighting on the side of Eadgils (Adils) in Sweden.
We learn further that about the time of Hygelac's death strife broke out in the royal family of the Svear, between Onela, the son and successor of Ongentheow, and Eanmund and Eadgils, the sons of his brother Ohthere.
The latter fled for protection to the Guar and the war which ensued cost the lives of Eanmund and of Heardred the son and successor of Hygelac. According to the poem Beowulf himself now became king of the Gotar and assisted Eadgils in a campaign which resulted in the death of Onela and the acquisition of the throne by his nephew.
In this saga AOils (the Eadgils of Beowulf), son of Ottarr is one of the most prominent figures.