The nickname of Harald Gormsson, a king of Denmark and Norway.
"The historical figure known as Bluetooth was actually King Harald Gormsson of Denmark and Norway."
Bluetooth gets its name from a combination of "blue" and "tooth," which translates Old Norse Blátǫnn, referring to King Harald Bluetooth who united Danish tribes. The networking standard was named after him because his technology similarly unites computers and mobile devices into one network.