Alastor "Mad-Eye" Moody is perhaps the most famous Auror in the modern times of the Wizarding World, single-handedly responsible for capturing numerous wizard criminals. He is also said never to have killed his quarry, even when permitted to do so, unless he had no other choice. Moody's face is badly scarred; he has lost several body parts while fighting Dark wizards, including his left eye, lower left leg, and part of his nose; and he is cautious – some characters might say paranoid – in that he refuses to eat or drink anything which he himself did not prepare. He has replaced his missing eye with a magical one that can rotate 360 degrees and see through almost everything (including walls, doors, Invisibility Cloaks, and the back of his own head). He walks with a pronounced limp due to his prosthetic leg, and uses a walking staff. He frequently exclaims "Constant vigilance!" to encourage wizards to be on their guard against the dark arts, and keeps a number of devices in his office to alert him to the presence of potential enemies.
In Harry Potter and the Goblet of Fire, Moody is appointed as the new Defence Against the Dark Arts teacher at Hogwarts, coming out of retirement as a favour to Dumbledore. Shortly before the school year begins, however, Moody is attacked by Barty Crouch, Jr., who subdues him with the Imperius Curse and takes Polyjuice Potion to assume his appearance. He keeps the real Moody alive as a source both of Polyjuice potion ingredients and of personal information helpful in putting the impersonation over, and takes Moody's place at Hogwarts teaching Defence against the Dark Arts. Moody's well-known habit of carrying around his own drinks in a private hip flask allows Crouch to take the Polyjuice Potion as needed without raising suspicion. Crouch/Moody becomes noted for teaching and demonstrating normally higher-level topics to Harry's fourth-year class (such as the Unforgivable Curses), being a demanding teacher who expects students to work, as well as punishing Draco Malfoy by transforming him into a ferret to stick up for Harry when Malfoy was tormenting him. Crouch/Moody also mentors Harry, encouraging and tutoring him in the three Tournament tasks. After Harry unexpectedly returns alive from the graveyard battle with Voldemort, Crouch/Moody takes Harry back to his office, questions him about Voldemort and the graveyard, and reveals that he is working for Voldemort. He then prepares to kill Harry, but Dumbledore, McGonagall, and Snape stop him. Having neglected to take his hourly dose of Polyjuice potion, Crouch transforms back to his own appearance and, under the influence of Veritaserum potion, confesses everything. Dumbledore then rescues the real Moody from his magic trunk.
In Harry Potter and the Order of the Phoenix, the real Moody has joined the newly re-formed Order, and leads the party transferring Harry from 4 Privet Drive to Number 12 Grimmauld Place. He appears at the climax of that book, arriving to the battle at the Department of Mysteries after being tipped off by Snape. He also appears with Lupin and Tonks at the very end, when they give the Dursleys a warning concerning their treatment of Harry. Moody's only features briefly in Half-Blood Prince. In Deathly Hallows he is killed by Voldemort after being abandoned by Mundungus Fletcher, who is acting as a decoy. The survivors are unable to recover his body, but later his eye is found by Harry upon Dolores Umbridge's door, being used by Umbridge to spy on Ministry of Magic employees. Harry retrieves the eye, disgusted that it would be used in such a way, and later buries it at the base of an old tree in Mad-Eye's memory.
Moody is portrayed by Brendan Gleeson in the film series.