In the tenth century a group of them were actually incorporated into a royal guard by the emperor Basil II, as he (probably wisely) didn't trust the native military, and the Byzantines respected the Scandinavians' martial skills. They were called the Varanngian Guard. I want to say that "Varanngian" loosely meant "The sworn ones"... but I think its also the term the Byzantines used for the Norse in general.
Thanx