Inviiktuz was a dragon, his name translated to 'Master, Defeat, Blade' in the Dragon Language.
In ancient times he sought to usurp Alduin, but he was cast into Oblivion by his brother. Specifically Malacath's plane of Oblivion, the Ashpit. Where he languished, chocking on the ash of the Prince of Pariah's and the Spurned's realm. During the Fourth Era, he was rescued from this torment by the Last Dragonborn, in an act of gratitude and humility he sworn fealty to the Dovahkiin.
He went on to serve the Dragonborn during the War of the Dragon Emperor, leading his kin against the Aldmeri Dominion. Not only out of loyalty for his savior. But because he knew that the Thalmors desire to unmake Nirn was against the will of Akatosh, and a general disdain for the High Elves in general.