Its source is Hrothgar, an Ancient Germanic name meaning "Famous spear."
This boy's name is used in Dutch.
When the Norman French defeated the Anglo-Saxon army at the Battle of Hastings in 1066, the victory they won for their Duke William was also a victory for French names. In some cases, old Anglo-Saxon names were forced to yield their place to upstart French names that were their own descendants.
Such was the case with Hrothgar, Germanic ancestor of the French name Roger. As Hrothgar faded into history, Roger was propelled into the future, spawning such nicknames as Hodge and Dodge (which survive in the surnames Hodges and Dodgson), and eventually joining the jet age as the universal acknowledgment of a radio message -- ''Roger!''