In the documentation produced by the English monarchy during the tenth century the Latin title imperator surprisingly appears, but it is not the first time that this title has been associated with an insular king. In Adomnán of Iona's Vita sancti Columbae (c.700), St. Oswald king of Northumbria appears as totius Britanniae imperator. Oswald, one of seven kings—successively called bretwaldas in the Anglo-Saxon Chronicle—who would have enjoyed a certain overlordship above other kingdoms of the island, could be the missing link connecting the use of the title imperator in the eighth and in the tenth centuries. Nevertheless, a closer view on the Oswald figure points out how he was remembered and worshipped more as a saint-overlord than as an emperor. Indeed, we can distinguish two different types of representation of the Northumbrian king’s authority: the first one proposed by Adomnán (emperor of Britain) and the second proposed by Bede (saint-overlord). In this article I show how the Bedian model had a greater diffusion than the Adomnán model in England in the following centuries, thanks to the cult of Oswald as a saint. This suggests that there was no direct link between the use of imperator in Adomnán and that in the tenth-century charters; they were two different manifestations of “imperiality.”