False Conflations of the Makhir of Narbonne Legend
As described more fully in Space: Legend of Makhir of Narbonne, Arthur Zuckerman  proposed, with no tangible evidence, that the following persons were the same. Nathaniel Taylor  identifies the conflation, with legendary persons in italics:
'Saint' William, son of Theuderic (in charter of 804) and Alda, count of Toulouse, 789, conquered Barcelona 801/3, founded the monastery of Gellone, 804, became a monk there, 806
Isaac, elder of Narbonne (Gesta Karob Magni...)
Isaac, royal ambassador to Harun al Rashid, 797-802
"Guiloume d'Orange" (chanson de geste), supposed son of 'Aymeri' de Narbonne
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The Liber Historiæ Francorum names "Theudericum…filium Dagoberto iunioris" recording his succession and reign of six years. 
He was born around 712  He was the son of king Dagobert III; his date of birth is not well known but after 711. 
Theuderic IV is given, in legend, the parents Haninai and [[Aquitaine-175|Rolinde.
After being taken from the monastery of Chelles, Charles "Martel" installed him [30 Jan/13 May] 721 as THEODERICH IV King of the Franks. He was not replaced as King of the Franks until six years after his death.
During his reign, his realm was controlled by the mayor of the palace, Charles Martel, who kept him in custody, first in Chelles Abbey, then in Château-Thierry. </ref name="wiki"/>