Nibelung, king of the Nibelungen, a mythical Burgundian tribe, the fabulous possessor of a hoard of wealth so inexhaustible that "twelve waggons in twelve days, at the rate of three journeys a day, could not carry it off," and which he bequeathed to his two sons on his deathbed, by the vanquishing of whom the hoard fell into the hands of the redoubtable hero Siegfried.