Eadgils, Adils, Aðils, Adillus, Aðísl at Uppsölum, Athisl, Athislus or Adhel was a semi-legendary king of Sweden, who is estimated to have lived during the 6th century.
Beowulf and Old Norse sources present him as the son of Ohthere and as belonging to the ruling Yngling (Scylfing) dynasty. These sources also deal with his war against Onela, which he won with foreign assistance: in Beowulf he gained the throne of Sweden by defeating his uncle Onela with Geatish help, and in two Scandinavian sources (Skáldskaparmál and Skjöldunga saga), he is also helped to defeat Onela in the Battle on the Ice of Lake Vänern, but with Danish help. However, Scandinavian sources mostly deal with his interaction with the legendary Danish king Hrólfr Kraki (Hroðulf), and Eadgils is mostly presented in a negative light as a rich and greedy king.
The Norse forms are based an older (Proto-Norse) *Aþagīslaz (where *aþa is short for *aþala meaning "noble, foremost" (German 'adel') and *gīslaz means "arrow shaft"). However, the Anglo-Saxon form is not etymologically identical. The A-S form would have been *Ædgils, but Eadgils (Proto-Norse *Auða-gīslaz, *auða- meaning "wealth") was the only corresponding name used by the Anglo-Saxons. The name Aðils was so exceedingly rare even in Scandinavia that among almost 6000 Scandinavian runic inscriptions, it is only attested in three runestones (U 35, DR 221 and Br Olsen;215).
The Anglo-Saxon epic poem Beowulf, composed sometime between the 8th century and the 11th century, is (beside the Norwegian skaldic poem Ynglingatal from the 9th century) the oldest source that mentions Eadgils.