Durnehviir

"My claws have rended the flesh of innumerable foes, but I have never once been felled on the field of battle."

- Durnehviir

 ( in dragon language) is an undead Dragon who resides in the Soul Cairn.

Background
Some time up to the early First Era, Durnehviir lived amongst his kin in the skies above Tamriel.

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 realm's 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.

The Ideal Masters deceived Durnehviir, as Valerica was a vampire, and thus also immortal. As a result, Durnehviir was doomed to guard the Soul Cairn for eternity.

Appearance
Durnehviir is unique in appearance, and does not appear to be of any breed of Dragon previously encountered. His body bears a resemblance to the Frost Dragon, with massive protruding spikes from the back of his neck and extending down to his tail. Four curved horns sprout from his head.

As an undead Dragon, Durnehviir's flesh is greatly decayed and his wings look extremely weathered. He is grey-green in complexion, and his scales are constantly dripping and oozing. Flies can be seen around his body, and yellowish drool can be seen constantly dripping from his mouth.

When he is defeated by the Dragonborn, his body burns with a unique, purplish fire, though his Dragon Soul is not absorbed.

Beyond Death
Before receiving the Elder Scroll from Serana's mother Valerica, the Dragonborn is attacked by Durnehviir on the way into the Boneyard. During the battle, his unique Dragon Shout can summon several Bonemen to his aid. After he is defeated, his body burns and he disappears; Valerica warns that he is unable to truly die and may reappear.

After exiting the Boneyard, Durnehviir is found waiting outside. He tells the Dragonborn that he/she was a worthy adversary and calls him/her "Qahnaarin," or "Vanquisher" in Dragon Language. If the Dragonborn has not yet killed their first dragon in the main questline, Durnehviir will say that it was his instinct to call the hero "Dovah" and that time will possibly clear it out for both of them. If the Dragonborn has finished the main game's quest line, he will speak about how he heard of the Dragonborn slaying Alduin, the World-Eater. He then explains how he was fooled by the Ideal Masters into becoming trapped in the Soul Cairn for eternity.

Summon Durnehviir
He also explains that he wishes to fly through the skies of Tamriel once again, but that his ties to the Soul Cairn prevent him from leaving for long periods of time. He thus teaches the Dragonborn the Summon Durnehviir shout to summon him.

The first three times he's summoned, he will teach the words for his Dragon Shout, Soul Tear. As with all shouts, they must be unlocked with acquired dragon souls.

1st summon
Ah! The free air of Vus at long last. As promised, I now teach you the first word of Soul Tearing: "" - the essence of your enemy's life force.

2nd summon
I can feel my strength returning each time I am set free from that prison! Hear now the second word of Soul Tearing: "" - meaning to tear your enemy's soul from its living vessel.

3rd summon
You have kept your side of the bargain, now let me fulfill mine. Feel the last word of Soul Tearing within yourself: "" - the unlife that results when a soul is imprisoned in dead flesh.

After this, whenever summoned in Skyrim, Durnehviir can aid the Dragonborn in battle. Durnehviir is the only Dragon able to use a unique shout that lets him summon Bonemen, Mistmen, and Wrathmen. The name of the Shout is Soul Cairn Summon, and the words of power are DIIL QOTH ZAAM (Undead, Tomb, Slave).

Notable quotes

 * "There was a time when I called Tamriel my home. But those days have long since passed."
 * "The Soul Cairn has become a part of what I am. I could never fully call Tamriel my home again, or I would surely perish."

Trivia

 * His name means "Curse Never Dying".
 * The above quotes, respectively, are as follows when translated into Dovahzul:
 * Til lost tiid fod Zu'u called Taazokaan dii bodein. Nuz den sul lost lingrah ruzun (passed).
 * Faal Sil (Cairn) has meyz goor do fos Zu'u los. Zu'u vust neh jahr for Taazokaan dii bodein einzuk, uv Zu'u fund bekgaar saluk.
 * If Dragon Rising has been completed, Durnehviir will recognize the Dragonborn as the "Dovahkiin". If the main questline for has been completed he will also recognize that Alduin was slain.
 * If Dragon Rising has not been completed, he will say he does not know why he calls the Dragonborn "a fellow dov".
 * If summoned in Skuldafn during the quest The World-Eater's Eyrie, he will frequently say "Skuldafn fen kos dinok" in the voice of other dragons, directed at the player.
 * Durnehviir does not resist Bend Will, but rather does not even register it.

Bugs

 * If called immediately with Summon Durnehviir while in Soul Cairn, Durnehviir will then act as if he's been summoned in Tamriel and then continues to teach the Dragonborn the Soul Tear Shout. If used right next to Durnehviir in the Soul Cairn immediately after learning the Shout, there will be two Durnehviirs in the area.
 * If the Dragonborn shoots and kills Durnehviir with a bow or crossbow right after he leaves the boneyard before  getting close enough for Durnehviir to speak, he is killed and the quest to learn a new shout is missed.
 * As he is summoned the player may get stuck inside him, unable to get out.
 * While fighting Durnehviir, if all his health is drained while he is on a perch, he will not fade away. Loading a previous save is the current solution.