Harald "Bluetooth" Gormsson so named because he had a blue tooth. He united the areas we call Denmark, Sweden and Norway. Not sure he would have called himself a Dane, or even a Viking. But we would call him a Viking or Scandiwegian.

The confusing thing is a lot of adverts refer to bluetooth devices as BT compatible. And BT is a large UK telephone company that was once nationalised. Some communication devices can be BT compatible in either/or sense!