Guillaume of Jumièges names “Rodbertum...Willelmum Suessionensem comitem atque Hugonem Luxoviensem præsulem” as the three sons of “ducis uno ex patre fratrem progenitum...Willelmum” and his wife “Lezscelinam...filiam...Turchetilli”, adding that Robert succeeded to his father’s county. He is named as the son of Guillaume Comte d'Eu by Orderic Vitalis. Robert’s date of birth is estimated from his having three sons who are named in a charter dated 1036. The date is consistent with his father’s estimated birth date, although it means that he must have been extremely old when he died. "Robertus comes Augensis…uxore Beatrice et filiis meis Radulfo, Willermo atque Roberto" made donations to the abbey of St Michel, Tréport by a charter dated 1036, witnessed by "Hugo vicecomes". An undated charter, dated to the [1035/50], records the donation of "predium Heltonis quod possedit Gozelinus vicecomes" to the abbey of Sainte-Trinité at Rouen, with the support of "Willelmus comes Normanniæ, et Willelmus, filius Willelmi comitis, qui et hæres Heltonis, et Robertus comes frater eius…Niellus…et Turstinus vicecomites", subscribed by "…filii Turchitilli Hugo et Goffridus necnon Walerannus comes", signed by "Gozelini vicecomitis, Heltonis, Willelmi heredis Heltonis, Walberti fratris Heltonis, Waleranni comitis, Alberici comitis, Heltæ filii Heltonis…". An undated charter, dated to , records that "Lezelina comitissa…cum filiis suis" was expelled "de castro Ou" and donated land on the banks of the Seine to Sainte-Trinité de Rouen, with the consent of "filiis suis Hugone, Willelmo, Rotberto".
He succeeded his father as Comte d'Eu, indicating presumably that he was the eldest son. Orderic Vitalis names “...Rodbertus comes, Willermi Aucensis Satrapæ filius...” among the leading lords under Guillaume II Duke of Normandy. "Rotbertus comes de Ou et Beatrix conjux eius" donated "jure hereditario silvam de Spinei" to Sainte-Trinité de Rouen, with the consent of "filiis suis", by undated charter dated to "tempore que discordia cepit inter [Willelmus comes Normanniæ] et Henricum regem Francorum", witnessed by "…Willelmi filii Osberni, Rodulfi camerarii…Goisfredi filii Osberni de Ou, Ansfredi fratris eius, Widonis filii Amalrici, Rainaldi de Sancto Martino, Osberti de Albert Villa…". "Rotberti comitis de Auco" witnessed a charter of "Rogerius de Buslei" dated 1053. Robert of Torigny's De Immutatione Ordinis Monachorum records that "Lecelina comitissa Aucensis relicta Willermi comitis" founded "mon. Sancti Petri super Divam virorum et mon. fem. ante urbem Lexoviensem" with "filiis suis Roberto comite Aucensi et Hugone episcopo Lexoviensi". The Brevis Relatio de Origine Willelmi Conquestoris records that "Roberto comite Augiensi" contributed 60 ships towards the invasion of England in 1066. Orderic Vitalis records that “Rodbertus Aucensium comes et Gauterius Gifardus et Radulfus de Mortuomari” and nearly all the seigneurs who lived “trans Sequanam usque ad mare” joined King William II against his brother Robert Duke of Normandy and received considerable sums to fortify their castles, dated to [1089/90].
The necrology of Saint-Nicaise de Meulan records the death of "Robertus comes Aucensis", undated but listed among deaths recorded in early September. The necrology of Ulterioris Portus monastery records the death "8 Sep" of "Robertus comes Augensis hujus ecclesiæ fundator". 2