Undead They are less a singular group and more of a category of creations made from the bones and flesh of the formerly living and imbued with life by granting them a modicum of their former feelings. The attitude and personality of an undead is dominated by the chosen feelings.
There are a myriad of undead creatures, many are feral creatures that are slave to their haunted emotions, others are aware and act as any other living creature.
Their creation is considered an abomination by many of the deities in particular Nepthys who sees them as violating the ancient cycles of life and death. Anubis's actions are responsible for the presence of Undead in Atum.