Draugr

When a ghost or spirit, in hatred, returns to its interred corpse and possesses the body to enact its vengeance, it becomes a type of undead known as a draugr.
The body of a draugr is withered and emaciated but not entirely skeletal It has deathly blue-black skin and eyes that glow with a spectral blue light in the darkness. For a corpse to become a draugr, the body must be well- preserved, whether by ritual interment, warding magic, mummification, or even the cold of ice and snow.

Animated By Hatred

Regardless of what drove them in life, in undeath, a draugr is motivated primarily by an overwhelming and unrelenting hatred. Most draugr lose any trace of their old nature as a living person, thinking and feeling only in terms of spite and enmity. If they are part of a group of undead, they might also feel a kind of obedience or even fearful respect for their undead lords. All draugr retain some semblance of old memories, no matter how deteriorated, from which they draw hatred Those who are animated by a particularly personal or bitter grudge often retain more of their personality and even their wits, using these traits to enact a devastating revenge on their most hated enemies.
The hatred that animates a draugr is so powerful and intense that it radiates through their spectral gaze. Just locking eyes with one can be enough to fill the bravest of warriors with a paralyzing ghastly terror.

Eternally Recurring

A draugr must be destroyed in a special manner to prevent it from returning and finally send it to its eternal resting place. It must have its head removed, and both the head and body must be burned to ashes. Finally, the remaining ashes must be poured into the brine of the sea directly. If this is not done, a draugr that is slain will inevitably return when its ghostly spirit finds its way back to where it was first interred.
One legend tells of a warrior, Olaf Eighth-Blade, who was killed in a drunken brawl by his brother Uldrik. The following year, when Olaf returned as a vengeful draugr, Uldrik slew the undead yet again. Thinking the danger had passed, he left for a raiding voyage. When he came back, he found that Olaf had returned, tricked his family to gain entrance, and slaughtered them in their home.

Guards of Tomb & Mound

Draugr are often found in the very tombs and burial mounds that they were buried within, motivated by a hatred for those who killed them in battle, guarding against anyone who would trespass on their tomb. Such draugr usually persist for eons, as even adventurers rarely have the time to dispose of the draugr properly in the sea. When adventurers destroy all the draugr within a tomb, the same draugr will likely return to guard the place again within a fortnight.

Lords of the Dead

When a powerful leader, hero, or warrior returns from the dead as a draugr, they may rise as a formidable draugr lord, capable of commanding the obedience of other undead using their malevolent glare. Draugr lords are often found deep within the tombs of legendary warriors or ancient kings, leading a group of draugr as loyal protectors of their lord's burial grounds.