From Wikipedia, Gilbert, Count of the Maasgau:

Gilbert (Giselbert), Count of Maasgau, was a vassal of Charles the Bald. He was count of Maasgau on the lower Meuse.
Gilbert's background is not known. The similarity of his son's name to the name "Ragnar" has been used as an argument to suggest a Viking connection.[1] Another possibility is that he was related to a man named Reginar, son of Meginhere (a nobleman from the court of Charlemagne).
Gilbert had served King Lothair I, but defected to Lothair's half-brother Charles the Bald during the civil war of 840-843. Gilbert's lands eventually came under the rule of Lothair and his rights as count were revoked. In 846 Gilbert abducted an unnamed daughter of Lothair and his wife Ermengarde of Tours. He took her to Aquitaine and married her in an attempt to force Lothair to reinstate him.[2] Rösch suggests that Gilbert's wife was named Ermengarde, but there is no conclusive evidence that this is correct.[3]
Children may include:
• Reginar, Duke of Lorraine (c. 850–916). There is no primary source unequivocally stating that Reginar was Gilbert's son. (emphasis added)
• Albert is mentioned as a brother of Reginar.[4]

References
1. McKitterick, R. (1983) Frankish Kingdoms under the Carolingians 751-987 (Longman, London and New York) p. 230.
2. Eric Joseph Goldberg, Struggle for empire: kingship and conflict under Louis the German, 817-876, Cornell University Press, 2006
3. Rösch, S. (1977) Caroli Magni Progenies (Verlag Degener & Co, Neustadt an der Aisch)
4. Halkin, J. and Roland, C. J. (eds.) (1909) Recueil des Chartes de l'abbaye de Stavelot-Malmédy, Tome I (Brussels)