The Annales Hanoniæ name "Raginerus" as son of "Raginerus [filius Ragineri dicti Longi-colli]". "Otto…rex" confirmed the possession of Kloster Süsteren by Prüm abbey by charter dated 1 Jun 949, signed by "Cuonradus dux, Herimannus dux, Hezzo comes, Godefridus comes, Rudolfus comes, Reginherus comes".
He succeeded his father as Comte de Hainaut, although the date he took control of the county is not known. "Ragineri comitis…" signed the charter dated to [936/57] under which "Adhelardus et conjux mea Fulcuera" donated a serf to the abbey of Saint-Ghislain. In 956, Reginar seized Brussels and the surrounding areas which had been the dower of Gerberge Queen of France on her first marriage to his uncle Giselbert Duke of Lotharingia. King Lothaire, together with Bruno Archbishop of Köln, invaded Count Reginar's territory, captured his fort on the Chier and took his family prisoner, releasing them only after Reginar returned the land which he had taken. The Gesta Episcoporum Cameracensium records that Reginar was banished to Bohemia in  by Archbishop Bruno, but was later reinstated in Hainaut by Otto II King of Germany. 1