The Lord of the Rings was chock-full of otherworldly figures. Elves were immortal beings, and some of them had been to the undying realm of Valinor. Meanwhile, Gandalf and the other wizards appeared as old Men, but they were actually primordial beings who were sent to Middle-earth by LOTR's angelic beings. However, not all the otherworldly beings in The Lord of the Rings were forces for good. Some of them were terrifying, and others were downright deadly.
Besides Sauron and his Nazgûl, the scariest thing in Middle-earth might have been the Army of the Dead. Originally Men of Dunharrow, they were supposed to serve Isildur during the War of the Last Alliance, but they fled into the mountains and hid. So, Isildur cursed them to never find peace. While the Army of the Dead inspired fear in The Return of the King, The Fellowship of the Ring's Barrow-wights were far more deadly. Here's the difference between the two groups of spirits.
What Were LOTR's Barrow-wights?
Barrow-wights never appeared in the LOTR movies. They were in the first half of The Fellowship of the Rings book, so they were cut along with Tom Bombadil. However, that doesn't make them any less interesting. The Barrow-wights lived in the Barrow-downs -- the oldest burial ground of Men in Middle-earth -- which was located in between the Shire and Bree. Yet the Barrow-wights had nothing to do with the spirits of deceased Númenóreans or Dúnedain Rangers. They were sent by the Witch-king of Angmar.
During the Third Age, the Witch-king made war on the three subkingdoms of Arnor. They fought valiantly for decades, but eventually, the evil forces were too much for the kingdom of Cardolan. Overwhelmed, the people of Cardolan fled to the Barrow-downs and entrenched themselves there until the Great Plague completely decimated them. That's when the Witch-king acted. He was still warring with the Kingdom of Arthedain, so he sent evil spirits to the Barrow-downs to ensure that the area would never be repopulated. Those spirits became known as the Barrow-wights.
How the Barrow-wights Differed From the Army of the Dead
In The Return of the King movie, Aragorn used the Army of the Dead to save the day in the city of Minis Tirith, but that's not actually what happened. In the book, the Army of the Dead only assisted at the Battle of Pelargir, and even there, they were only used for a scare factor. They were merely cursed spirits, so they couldn't do anything physically or actually harm anyone or anything. However, that was not the case with the Barrow-wights.
The Barrow-wights were dark phantoms with glowing eyes, but their worst quality was their hypnotic voices. Using their voices, the Barrow-wights would lure victims into the tombs, put them on stone alters and bind them with golden chains. After dressing the victims in pale cloth, the Barrow-wights would execute them with a sacrificial sword. That's nearly what happened to Frodo and the other Hobbits. Luckily, Frodo mustered enough courage to cut off the Barrow-wight's hand and call for Tom Bombadil's powerful aid. Why the Barrow-wights were able to interact with the physical realm wasn't clear, but it had something to do with the remnants of the Witch-king's evil magic.