Alastor Moody's magical eye

Alastor Moody's magical eye acted as a replacement eye for him after he lost his original one in battle. It is a round, electric-blue eye that he placed into his empty eye socket. It can rotate 360 degrees in Moody's head and allowed him to see through anything, whether it be wood, Invisibility cloaks, or even the back of his head. However, there appeared to be limits, since Albus Dumbledore was presumably able to cast a Disilliusionment Charm so strong that it cloaked not just him but also Professors McGonagall and Snape from Barty Crouch Jr's perception when they apprehended him. It is this eye that earned Moody his nickname "Mad-Eye."

First Wizarding War
Sometime during the First Wizarding War, Moody lost his eye during a clash with Death Eaters, and had the magical glass eye inserted as a replacement.

1994-1995
During summer 1994, before Moody was able to take his one-year post as Defence Against the Dark Arts teacher of Hogwarts School of Witchcraft and Wizardry, he was attacked and captured by Peter Pettigrew and Barty Crouch Jr. Using Polyjuice Potion, Crouch Jr. disguised himself as Moody and then took Moody's eye and leg as his own.

"Damn it, it keeps getting stuck — ever since that scum wore it."

- The damage the eye suffered from Crouch's wearing.

After Moody was freed and regained his eye, the eye tended to get stuck in mid-rotations at times, due to Barty Crouch having worn it. Moody had to put the eye in water and clean it to get it to function properly once more.

1997-1998
In July 1997, Moody was killed by Lord Voldemort during the Battle of the Seven Potters. Moody's corpse was recovered by the Death Eaters, and his magical eye was taken by Dolores Umbridge, who used it to keep track of her subordinates in the Ministry of Magic.

When Harry Potter, Hermione Granger, and Ron Weasley broke into the Ministry, Harry found the eye and was revolted by how it was being used. He took it off its wall, which raised alarm. After the trio fled from the Ministry and to the forest near where the 1994 Quidditch World Cup was held, Harry buried the eye under the oldest, most gnarled and resilient-looking tree he could find, and marked the grave with a small cross. With this, Moody was given a proper burial, as far as was possible.

Behind the scenes

 * In the novels, the magical eye replaced Moody's right eye. In the films, it replaced his left.
 * In the books, the eye has been depicted to be simply to be inserted into his empty eye socket. In the films, it requires some special holder strapped around the socket.
 * In the fourth film, the eye has shown to also have zoom-in capabilities.
 * It is unknown if this eye is unique to Moody, or if anyone can get one if they needed an eye-replacement, although the fact that it is powerful enough to see through the Cloak of Invisibility, one of the Deathly Hallows, suggests that it may be a rare artefact or, at least, not commonly found or produced.
 * Although the magical eye was seen as a cameo on the door of Dolores Umbridges office following Moody's death in Harry Potter and the Deathly Hallows: Part 1, there is no indication of Umbridge receiving it as a gift. Additionally, the parts of Umbridge using the eye to spy on the Ministry workers, Harry learning it is there and retrieving it, as well as Harry burying the magical eye out of respect for the late Moody, have been omitted.
 * In LEGO Harry Potter: Years 1-4, Moody's eye is like his normal eye in colour, though larger than his normal eye and held up by a strap.
 * In LEGO Harry Potter: Years 5-7 Moody's eye is much larger and Harry and Ron as Cattermole and Runcorn must make a violin out of Diffindo pieces and lull the eye to sleep, then sneak in.

Appearances

 * Harry Potter and the Goblet of Fire
 * Harry Potter and the Goblet of Fire (film)
 * Harry Potter and the Goblet of Fire (video game)
 * Harry Potter and the Order of the Phoenix
 * Harry Potter and the Order of the Phoenix (film)
 * Harry Potter and the Order of the Phoenix (video game)
 * Harry Potter and the Half-Blood Prince (film)
 * Harry Potter and the Deathly Hallows
 * Harry Potter and the Deathly Hallows: Part 1
 * LEGO Harry Potter: Characters of the Magical World
 * LEGO Harry Potter: Years 1-4
 * LEGO Harry Potter: Years 5-7
 * Harry Potter LEGO Sets

Notes and references
Œil magique d'Alastor Maugrey