"Undead" refers to dead beings who could still interact with the living. By the Third Age, the Rohirric word "Dwimmerlaik;" meaning "Spectre" or "Work of Necromancy", was used as a catch-all term.
- Barrow-wights were evil spirits inhabiting the tombs of the Barrow-downs. They often possessed the grave-gifts and bones of those entombed there, making them similar to the animate skeletons of other works.
- Ghosts (the Army of the Dead, specifically) are the souls of the dead who are prevented from reaching their final rest. The largest concentration were the dead warriors who betrayed Isildur and were cursed, haunting the mountain until Aragorn persuaded them to fight for him. Their faces often shift from skeletal frames to pasty shadows of themselves. Gorlim the Unhappy might be considered one too.
- Nazgûl or Ring-Wraiths: Formerly Kings of Men, the nine rings gifted to them by Sauron caused them to become ghost-like Wraiths. They cannot see properly, and rely on smell and hearing. The Nazgûl carry daggers known as Morgul-blades meant to break off in the wound, which can turn the afflicted into a wraith. Frodo was stabbed by one at Weathertop. However, it is mentioned that Nazgul are not properly undead.
- Wraiths were humans (Dwarves had natural resistance) who come into possession of a Ring of Power and wore it too long, or were stabbed by a Morgul-blade. They were permanently invisible, and more or less immortal.
- Phantasms were delusions and/or spirits or fallen Maiar and therefore not truly undead. Morgoth and Sauron used them for their treachery. It is said Saruman also used them.
- Lingerers are elves whose bodies have been consumed by their fëa. To men, they are indistinguishable from bodiless spirits. These elven spirits are not really undead, because they were never dead to begin with.
- "The Houseless" were ghosts of slain elves who were evil, hateful or otherwise sinful in life and defied the call of Mandos. These elven ghosts had the unique ability to possess living things; most often they desired to steal the bodies of Men to become material again, but according to some, they also could possess anything alive. Old Man Willow may have been possessed by one of the Houseless.
There may also have been some form of undead residing in the Dead Marshes
There are many of these fearsome creatures in the Barrow-downs where the Witch-king of Angmar himself went when he was looking for the One Ring in The Shire. For his evil presence, the ancient spirits were raised again killing people with their ceremonial swords and bringing the terror with them.
Portrayal in adaptations Edit
The Games Workshop tabletop wargame mentions the Castellans of Dol Guldur, animate suits of armor possessed by the ghosts of people tortured to death in the fortress' dungeons, or whom agreed to be bound to Sauron's will in exchange for learning sorcery from him.
The Lord of the Rings tabletop RPG Middle Earth Roleplaying by Iron Crown includes skeletons and ghouls among certain other types.
The Return of the King tie-in licensed videogame featured the Army of the Dead being able to possess ossuaries to form skeletal soldiers. These are the majority of the enemies one fights in Dunharrow. The King of the Dead is the level boss; able to summon skeletal archers, warriors, and a powerful blast of wind able to spit stone.