Notes

Rachel R. Raine (Slytherin)

Imperius Curse
The Imperius Curse (Imperio) is a tool of the Dark Arts and one of the three Unforgivable Curses. It is one of the most powerful and sinister spells known to wizardkind. When cast successfully, the curse places the victim completely under the caster's control, though a person with exceptional strength of will is capable of resisting it.
The fact that the curse can be defended against makes it unique amongst the Unforgivable Curses. It is also unique in that it is the least harmful of the curses (unless one counts the complete lack of free will) except if performed improperly.
The Imperius Curse was invented during the early Middle Ages by dark witches or wizards. The curse was created for the coercion and brainwashing of others into slavery.
After the Wizards' Council was reformed into the Ministry of Magic, tighter restrictions were placed on the use of certain kinds of magic. The Imperius Curse was deemed by the Ministry to be dark magic, and, along with the Cruciatus and Killing curses, were declared "unforgivable" in 1717. The use of any of these three curses on a fellow human being would result in a life sentence in Azkaban, unless there is sufficient evidence that the caster did so under the influence of another's Imperius Curse; this tends to be a loophole that many Dark Wizards abuse and lie about when they were facing prison time, particularly after the First Wizarding War.
Many Secret Keepers in the past have been subjected to the Imperius and Cruciatus Curses in an attempt to learn the secrets they keep, but to no avail as the Keeper must reveal it willingly.[1]

Unlike the other Unforgivables, being subjected to the Imperius Curse — when adequately cast — is not an unpleasant experience, in fact, quite the opposite; the victim of an Imperius Curse is placed in a calm, trance-like state in which all feeling of responsibility and anxiety is banished (drawing parallels to the real-world phenomenon of hypnosis, which is also often portrayed in fiction — albeit inaccurately[5] — of being capable of placing someone under the complete control of another by placing them in a theta state).
Resisting the Imperius Curse is possible, but requires great strength of will and character. The fact that it can be resisted makes it unique amongst the Unforgivable Curses as it is the only curse that has a manner of defence.