Harald may have had a conspicuously bad tooth or especially liked to eat blueberries, which would explain his epithet "Bluetooth". His reign, from about 958 to 985, was marked by more peaceful relations among previously warring Scandinavian tribes, which later Scandinavian chroniclers attributed to Harald's ability to mediate between hostile groups.
(Interestingly, during this same three decades, Anglo-Saxon England was also less ravaged by Viking invasions. Coincidence?)
Kardach liked to explore history and was intrigued by the career and aspirations of King Harald, so he did some more reading. During discussions among several tech companies with different proposals for wireless (radio) interfaces, he chose the name Bluetooth as an appropriate, if temporary, name for the special interest group they were trying to form. Previously, Intel, Ericsson and Nokia had each been developing separately a wireless technology to enable different devices to communicate with one another. As the project moved forward, the group adopted Bluetooth until a formal name was chosen. But the name stuck. While many internet names have been drawn from the cultural mythology of exploration, discovery and conquest (Explorer, Safari, Konquerer, Netscape Navigator), Bluetooth is linked to a story of communication and peace.