Durnehviir is an undead Dragon residing in the Soul Cairn, where he guards Valerica, Serana's mother under orders from the Ideal Masters. Durnehviir is a bit of an odd one amongst others of his kind while his brethren used more traditional forms of combat, Durnehviir pursued an interest in necromancy that eventually led him to the Ideal Masters. His wish was to raise armies of undead for his own ends, so he made a pact with the Ideal Masters to gain access to their realms undead. The pact specified that Durnehviir was to serve as the keeper of the Soul Cairn, and guard Valerica until her eventual death - terms to which Durnehviir, being an immortal dragon, agreed. But the Ideal Masters had deceived Durnehviir, as Valerica was a vampire, and thus also immortal. As a result, Durnehviir was doomed to guard the Soul Cairn for eternity.

In the dragon language his name is spelled using the words for Curse/DUR, Never/NEH, and Dying/VIIR

Unlike most Dragons however he is not so prideful that he would not ask a favor of the Dragonborn in exchange for his loyalty. Durnehviir has spent too long in the Soul Cairn and is now forever linked to it, he can however spend some time in the real world, if he is summoned there using his name as a shout. Durnehviir asks the Dragonborn so summon him so that he may once again soar the skies of Tamriel, and in exchange he will lend him his power.
durnehviir