The Genealogica Comitum Flandriæ Bertiniana names (in order) "Balduinum Haanoniensem, et Robdbertum cognomento postea Iherosolimitanum, et Matilde uxorem Guillelmi regis Anglorum" as the children of "Balduinum Insulanum [et] Adelam". "Robertus filius Balduini comitis Insulani" is named in the Cartulaire de Saint-Bertin. He is recorded by Orderic Vitalis as uncle of Robert de Normandie. The Annales Blandinienses record that in 1063 "Rodbertus, Baldwini potentissimi iunior filius, Frisiam subintrat".
He was regent of the county of Holland 1062-1071, during the minority of his stepson. He rebelled against his nephew Arnoul III Count of Flanders and defeated him at the battle of Cassel 22 Feb 1071, succeeding as ROBERT I "le Frison" Count of Flanders. He was recognised as count by Philippe I King of France after Robert transferred Corbie to him, the arrangement being confirmed by the king's marriage to Count Robert's stepdaughter Bertha of Holland. Relations with William I King of England were poor, culminating in Count Robert's planned naval attack in 1085, with his son-in-law Knud II King of Denmark, although the enterprise ended when the latter was assassinated.
William of Malmesbury records that Robert made a pilgrimage to Jerusalem, dated to between 1086 and 1090. On his way back, he entered the service of Emperor Alexios I.
The Annales Blandinienses record the death "III Id Oct 1093" of "Rodbertus, primus huius nominis Flandriæ marchysus". 1
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