Sorry, the following is the copy & paste from OP's earlier post that has been deleted.

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While there will always be more to be said, I posted a reply to similar question as OP's before in: Did Viking armies have a military rank structure? If so, what was it, and who was in charge or above who?

Viking Emperor

While the political dominion of Cnut the Great across the North(ern) Sea(s) is generally called "North Sea Empire" by researchers, AFAIK there was no Scandinavian who claimed himself an emperor from the 9th to the 11th centuries. Even for them, Old Norse keisari means either the emperor of the Byzantine empire or that of HRE. In Old Norse, the word keisari could sometimes also be replaced just with the king (konungr) in customary and aesthetic use, as Snorri comments in his poetic treatise section in famous Prose Edda, Skáldskaparmál as following:

"For it is normal to call the emperor of Constantinople king of the Greeks, and similarly the king that rules Palestine, to call him the king of Jerusalem; also to call the Roman emperor king of Rome.....(Snorri Sturluson, Poetic Edda, trans. Anthony Faulkes, London: Everyman, 1997, Chap. 53 (pp. 127f.)"

On the other hand, as I mentioned in the linked post, larger Viking fleet often comprises of smaller unit of ship(s) organized by the military retinue system of the Norse chieftains. So, in order to keep them loyal to so-to-speak 'general leader of the whole fleet', possibly 'Emperor' in OP's word, was not so easy. To give an example, the famous (notorious) Great Army in the 9th century soon dissolved after their most famous leader, Ivar, in 873.

As for how individual chieftain with a smaller size of the fleet conducted the raid, /u/sagathain's previous post in: I’m a Norse Jarl. I want to raid and pillage some English villages across the sea. How many men do I need? might also be interesting to you.