imperio - The Imperius Curse

The Unforgivable Curses are some of the most powerful Dark Arts spells known in the fictional world of Harry Potter. Commonly used by the villains, such as Lord Voldemort and the Death Eaters, their use inspires horror and great fear amongst others. The curses are so named because their use is - except by Ministry of Magic authorisation - forbidden and literally unforgivable in the Wizarding World. Use of any of these spells on any human being can carry a life-sentence in the magical wizard's prison of Azkaban. These curses are thus very rarely used openly. Since the spells are very powerful, their use requires a strong desire to bring about the effects, a directed will, and great skill.

The Imperius Curse places the subject in a trance or dream-like state, and leaves him or her subject to total control by the caster. The experience of being controlled by this curse is described as a complete, wonderful release from any sense of responsibility or worry over one's actions, at the price of one's free will. Resisting the effect of the curse is possible, however, and several individuals have been able to successfully stand against it, including Harry Potter, as well as both Bartemius Crouch Jr and Bartemius Crouch Sr, who learned to resist the curse after being subjected to its effects for an enduring period.

^{Source: Wikipedia}