Inferius

"They are corpses, Dead bodies that have been bewitched to do a Dark wizard's bidding. Inferi have not been seen for a long time, however, not since Voldemort was last powerful.... He killed enough people to make an army of them, of course."

- Albus Dumbledore on Inferi

An Inferius (plural: Inferi) is the dead body, reanimated by a Dark Wizard, similar to a zombie. They have no free will, and cannot think for themselves; their purpose is merely to serve as puppets of the Dark Wizard who reanimated them. They were used by Lord Voldemort in both the First Wizarding War and the Second Wizarding War. It is mentioned that the dark wizard Gellert Grindelwald also sought to create an army of Inferi. It is unknown as to whether he succeeded. Inferi are created through the magical branch of Dark Arts called Necromancy.

Defence against Inferi
Because Inferi are creatures of the dark, they dislike light and heat. The most effective spell against them is therefore a fire-summoning spell, such as Incendio, Lacarnum Inflammare, or Fiendfyre. Other spells might work against a few Inferi, but might not be useful against a whole army of them. It must be noted that Inferi are resistant to most spells: they cannot feel pain, and thus are unaffected by many attacks whose main effect is pain such as the Cruciatus Curse. This is evident when Harry Potter attempts to use the dark spell Sectumsempra on the Inferi in the Horcrux cave, as they have no blood to spill.

Encounters

 * In 1997, Harry Potter and Albus Dumbledore encountered this very same army of Inferi in their attempt to steal one of Voldemort's Horcruxes. Dumbledore successfully repelled them by conjuring a ring of fire, big enough to surround both Harry and himself.
 * Not exactly counted as a real encounter, but worth mentioning: Mundungus Fletcher was arrested and put into Azkaban because he disguised himself as an Inferius after being caught during a burglary.
 * The Ministry warned the community that Voldemort may be using Inferi once again in the Second Wizarding War, and he was mentioned that he did use as much as an army during the First War.
 * Harry Potter, Ron Weasley and Hermione Granger encountered some inferi during the Horcrux hunt. They were at an abandoned nuclear power plant, in the Forest of Dean and near the Lovegood house.
 * Regulus Black was most likely killed by Inferi in his attempt to destroy one of Voldemort's Horcruxes.

Etymology
"Inferius" is Latin for "underneath; below." It could also be a tampered form of "inferus", or "the dead; underworld." As J. K. Rowling sometimes changes real Latin words to form some incantations, or names of creatures or people, it could well be that the second meaning is the correct one.

Behind the scenes

 * According to W.O.M.B.A.T., Inferi may have the ability to speak.
 * Inferi may have been briefly referred to by Voldemort in the Little Hangleton Graveyard as part of an "army of creatures whom all fear".
 * Inferi may be incredibly strong as a picture in Snapes' DADA class shows a bloody mess on the floor, attributing to a person provoking the anger of an Inferius. Alternatively, this could be attributed to their visciousness and implacability.
 * It is unknown if there is any difference between Inferi and Zombies, as they are both reanimated corpses.
 * In first part video game adaption of Harry Potter and the Deathly Hallows, Inferi appears again, despite them not being in the mainstream storyline.
 * Inferi resemble Gollum from the Lord of the Rings trilogy.

Appearances

 * Harry Potter and the Half-Blood Prince
 * Harry Potter and the Half-Blood Prince (film)
 * Harry Potter and the Half-Blood Prince (video game)
 * Harry Potter and the Deathly Hallows
 * Harry Potter and the Deathly Hallows: Part 1 (video game)
 * The Tales of Beedle the Bard (real)

Notes and references
Inferius Inferius Inferi Инфернал Manalius