King Harald Bluetooth was a Viking king who ruled Denmark and parts of Norway during the late 10th century. He is best known for uniting the tribes of Denmark and converting them to Christianity, which helped to establish a more centralized kingdom. His reign marked a significant transition from paganism to Christianity in Scandinavia. Harald is also credited with the introduction of the first written laws in Denmark and the construction of fortifications, such as the famous Aarhus and København sites. The term "Bluetooth" in modern technology is named after him, symbolizing the unification of devices, much like he unified his kingdom.