Negative Magic

Unforgivable Curses?

The Unforgivable Curses are the three most powerful and sinister spells known to the wizarding world and are tools of the Dark Arts.  

Three curses in particular are known as Unforgivable because using them on another human being can result in a life term in Azkaban. These three curses were used extensively by Voldemort's followers during his rise to power in the 1970's, and their use by Aurors against suspects was in turn authorized by Bartemius Crouch Sr. at that time.

It's Impact to the Wizarding Society

Incantation: Avada Kedavra
 

This spell causes instant and painless death to the victim, leaving no physical signs as to the cause. There is no known counter-curse or blocking spell, but the spell can be blocked by physical cover which will be heavily damaged in the process, and the caster is still required to aim to hit the target. This spell produces a flash of green light. Just before it hits the target, a rushing sound that is similar to an oncoming high-speed object is heard.

Notable History: Only one person has ever been able to defeat the effects of the curse, even on a direct hit: Harry Potter who was given magical protection against Lord Voldemort's use of the curse through his mother's loving sacrifice. Harry was later saved by the effects of Priori Incantatem when his and Voldemort's wands locked during a duel in 1994.

Incantation: Crucio

This curse inflicts intense pain on the recipient of the curse. 

Notable History: It is the curse which caused the parents of Neville Longbottom such suffering that they were admitted to the permanent ward at St. Mungo's Hospital for insanity.

THE IMPERIUS CURSE

Incantation: Imperio

When inflicted, it places the subject in a dream-like state, in which he or she is utterly subject to the will of the caster. However, those who are strong willed may learn to resist it.

Notable History:  Harry Potter, Barty Crouch Sr. and Barty Crouch Jr. each learned to resist the curse after being subjected to its effects.