It is a legendary warrior from the continent of Tamriel and its province, Skyrim. During the second era the reformation of the Galts caused disturbances throughout the empire. This forced the high emperor to begin using Nordic warlords to engage the valdrani in pitched combat. Once the Nord's claimed victory they were honored atop the Jeralls and blessed with 18 unique aedra created weapons (one for each valyhaar). Gjallarhorn was the twelfth in the line of danthaar and was thus very powerful. Hope that clears it up you nerd!