#Linguistics Modern scholars think this nickname might be a reference to having bad teeth because the tǫnn part means tooth and the blá part meant black or blue. Harald, thus, is known in English as Harald Bluetooth. So there's that.

Harald Bluetooth had a wife named Gunhilde. This was also a very common name. In fact, he also had a daughter named Gunhilde. I don't know the exact meaning, but both bits of that name gave to do with war. +