Vemund
Brother of King Audbjorn who retained Firdafylke after his brother's fall, attested in two sources.
Vemund was King Audbjorn's brother who retained control of Firdafylke after the battle, attested in both the Heimskringla and Egil's Saga. The Heimskringla records that Vemund still held Firdafylke after the conflict (Heimskringla, Heimskringla > The Chronicle Of The Kings Of Norway > 12. King Vemund Burnt To Death.). Egil's Saga provides the same information with slightly different framing: Vemund became king of the Firthfolk after Audbjorn's death (Egil's Saga, Chapter 1 > Chapter 4. Battle of king Harold and Audbjorn.).
The two sources agree on the essential facts — Vemund was Audbjorn's brother and took control of Firdafylke after Audbjorn's fall — but frame his succession differently. The Heimskringla presents it as continuity: Vemund "still had Firdafylke" (Heimskringla, The Chronicle Of The Kings Of Norway > 12. King Vemund Burnt To Death.). Egil's Saga presents it as a new appointment: he was "made king" of the Firthfolk (Egil's Saga, Chapter 4). The distinction is subtle but telling — one suggests unbroken authority, the other a formal elevation.
Appears in: Beings, Cross-Source Entities, Norse Tradition