lived in Denmark between 910-940 AD, and was the son of Gorm. 

Contrary to popular opinion, Bluetooth or "Blåtand" as it was in old Viking language had nothing to do with a blue tooth. 

It means dark complexion – he had very dark hair, which was unusual for Vikings. Not only did Harald not fit the classic image physically, he was a rather unusual Viking. 

That is, if your understanding was that the life of a Viking was all battles and pillage. The good King Harald brought Christianity to Scandinavia and also "united" Denmark and Norway. And while we are destroying long-held beliefs, Vikings did not have horns on their helmets! 

Much of Harald’s history was learnt from two runic stones erected to his memory in the town of Jelling in Denmark.