One thing I know is that way back the Scandinavian word for slave was träl, or "thrall" in its English form. When you count in all the trade and raiding that went on over the Baltic and the so-called "East Route" (the Russian rivers that link the Baltic to the Black and Caspian Seas), and the curious similarity between the name Slav and the term "slave" (bluntly slav in Swedish, AFAIK), it gets a whole lot difficult to assume coincidence.

Wherever the name Slav originated from is then a whole another issue, but by what I've read the whole ethno-cultural concept developed under Avar overlordship during the Dark Ages. *shrug* A little irrelevant really, as we were discussing the political influence of Scandinavians (mostly Swedes; they plied the Eastern route, while the Norse and Danes went to Britain and Europe) in the riverside princedoms of southern Russia. Odds are the Vikings' considerable seamanship skills and good ships allowed them to pull some serious weight on the waterways and dominate trade, which would naturally also have make them desirable allies and partners to the local potentates (I understand the Khazars and Hungarian-Magyars were the big names around the period, although the latter eventually departed for Hungary). Political marriages or straight armed power grabs flow naturally from that, and usurpers in particular have since the dawn of history always been keen on whitewashing their background...