William the Conqueror spoke french. He and a lot of people in Normandy weren't vikings, they were only descended from norwegian or danish vikings that settled in what came to be Normandy somewhere between a 100 and 200 years earlier. It was Williams great-great-great-great grandfather Rollo (later baptised Robert) that founded the viking municipality that would later become Normandy. So William was more french than Norse, he just had Norse roots. Historians disagree on whether Rollo came from Norway or Denmark.
#2: The Normans spoke a dialect of French called Norman French. After the Norman conquest the same dialect was used by the ruling classes in England. Three hundred years later it had developed in England until its speakers could not understand 'French of Paris', according to Geoffrey Chaucer. Eventually its use died out in England, but a large part of its vocabulary had by then been absorbed into English. The English language has retained most of its Norman-French vocabulary to the present day, which we use alongside the Anglo-Saxon vocabulary.
As an example, the previous sentence used the word 'retained' from the French side, while it could also have used 'kept' from Anglo Saxon.