Imperio

The Imperius Curse is the third of the Unforgivables, and in many ways the strangest. It does not produce pain. It does not kill. What it does is take a person and quietly remove them — replace their will with the caster's, like reaching into a clock and adjusting the hands.

From the inside, the experience is described not as torment but as relief. The Imperiused person feels weightless, untroubled, gently happy. Worry evaporates. Conscience falls silent. A voice tells them what to do, and doing it feels right. That is the curse's particular evil: it doesn't break a person against their will, it persuades them not to have a will at all. Most witches and wizards under Imperius have no idea anything has happened to them.

Resistance is possible, but rare. A witch or wizard with a sufficiently strong sense of self can sometimes feel the dissonance between the order and their own thoughts and refuse the order outright. Harry famously throws off Imperius on his first attempt during Mad-Eye Moody's fourth-year DADA demonstration, which Moody flags as remarkable — most people, including most adult wizards, simply comply.

After Voldemort's first fall in 1981, dozens of prominent witches and wizards — Lucius Malfoy among them — claimed they had been acting under Imperius the entire war. Some of those claims were true. Others were a clever legal defense. The trouble with Imperius as a charge is that it is essentially impossible to disprove from outside. During the Second Wizarding War, Voldemort's Ministry takeover was held together largely by Imperius — Pius Thicknesse, the puppet Minister for Magic, was Imperiused throughout, and many lower officials never realized they were no longer making their own decisions.