Onela was, according to Beowulf, a Swedish king, the son of Ongentheow and the brother of Ohthere. He usurped the Swedish throne, but was killed by his nephew Eadgils, who won by hiring foreign assistance.

In Scandinavian sagas a Norwegian king by the same name exists, Áli (the Old Norse form of Onela, also rendered as Ole, Åle or Ale), who had the cognomen hinn Upplenzki ("from Oppland").

The name stems from the Proto-Norse Anulā, attested on the spear shaft SJy 68 from Nydam Mose. It is a diminutive with l-suffix to a name starting with *anu-, or directly of an appellative *anuz, "ancestor".

In the Anglo-Saxon poem Beowulf, Onela plays a central part in the Swedish-Geatish wars. Onela and his brother Ohthere were the sons of the Swedish king Ongenþeow. When the Geatish king Hreðel died, Onela and Ohthere saw the opportunity to pillage in Geatland starting the Swedish-Geatish wars:

The war ended with Ongenþeow's death.

It is implied by the poem that Onela eventually became king, because Ohthere's two sons, Eanmund and Eadgils, had to seek refuge with Heardred, Hygelac's successor as king of the Geats. This caused Onela to attack the Geats. During the battle, Eanmund was killed by Onela's champion Weohstan and Heardred was killed as well, after which Onela returned home.

Eadgils, however, survived and later, Beowulf helped him avenge Eanmund by slaying Onela.

By a conjectural emendation of line 62 of this poem some editors represent Onela as the son-in-law of Healfdene/Halfdan king of Denmark.