Oliver, a favourite paladin of Charlemagne's, who, along with Roland, rode by his side, and whose name, along with Roland's, has passed into the phrase, a “Roland for an Oliver,” meaning one good masterstroke for another, such as both these knights never failed to deliver.
Definition taken from The Nuttall Encyclopædia, edited by the Reverend James Wood (1907)
Olivarez, Count d' * Olives, Mount of