Ah yes, the Mind Controlling Curse. At one time this gave the Ministry quite a bit of trouble. This is another common spell used amongst Death Eaters. Like all the other Curses, this could give you a life sentence in Azkaban (you know, the Wizard prison) it is first used (in the Harry Potter series) on Viktor Krum on the Third Task of The Tri-Wizard Challenges.

Facts on the Imperius Curse:
Say: Imperio (pronounced: Im-peer-e-oh)
Wand movement: any
Color: Orange Light (formally Yellow)

Next chapter: The Cruciatus Curse