<P> The Unforgivable Curses are some of the most powerful known Dark Arts spells . They were first classified as unforgivable in 1717 . Used by the books' villains, such as Voldemort and the Death Eaters and in some cases the Ministry of Magic, their use inspires horror and great fear amongst others . The curses are so named because their use is forbidden and unforgivable in the wizarding world and is punishable by a life sentence in Azkaban . The only exception is if a person is proved to have done them under the influence of mind control . These curses are thus very rarely used openly . </P> <P> The Unforgivable Curses include: </P> <Ul> <Li> Avada Kedavra, the Killing Curse . The curse is used for murder . This is one of the most powerful curses . Normally, it cannot be stopped or deflected, but it can be dodged or obstructed with a physical object . The spell causes immediate, painless death, and cannot be reversed . Casting it requires immense magical power, so much so that the combined power of an entire class of 4th year students is not sufficient for it . The curse, when summoned, is shown as a bright green light (a bolt or beam of green light in the films). Harry Potter is the only person known to have survived (twice), nullified (once) and deflected (once) this curse . </Li> <Li> Crucio, the Cruciatus Curse . The curse is used for torturing a person by causing them physical pain and agony . The strength of the curse is determined by the person who cast it . The curse is so powerful that it can even torture a person to the point that they are exhausted to death, or in a more sadistic case, it causes permanent amnesia and insanity (the case of Neville's parents, who were tortured by Bellatrix Lestrange). Effective casting requires the caster to have sadistic desires . Harry finds out in Order of the Phoenix while attempting to use the Cruciatus Curse on Bellatrix that the caster must truly want their victim to suffer for the spell to work, and that his righteous anger is not enough . The curse, when summoned, is shown in a bright - faded blue light (though it is usually invisible or even a red bolt of light in the films). When Hogwarts was under Death Eater control, the Dark Arts teacher forced the students in his class to use the Cruciatus Curse on students who had been assigned detention . </Li> <Li> Imperio, the Imperius Curse . The curse is used for mind control or hypnosis and can force the victim to do things he / she would be unwilling to do or even incapable of under normal circumstances . The strength (and also the duration) of the curse is determined by the determination of the person who cast it, as well as by the level of resistance of the victim . The curse, when summoned, is shown in a bright haze (while it was either invisible or green, mist - like haze in the films). Harry Potter resisted an Imperius Curse cast by Voldemort . </Li> </Ul> <Li> Avada Kedavra, the Killing Curse . The curse is used for murder . This is one of the most powerful curses . Normally, it cannot be stopped or deflected, but it can be dodged or obstructed with a physical object . The spell causes immediate, painless death, and cannot be reversed . Casting it requires immense magical power, so much so that the combined power of an entire class of 4th year students is not sufficient for it . The curse, when summoned, is shown as a bright green light (a bolt or beam of green light in the films). Harry Potter is the only person known to have survived (twice), nullified (once) and deflected (once) this curse . </Li>

What is the killing curse in harry potter called