Moody was one of the best Aurors at the Ministry of Magic in his time, and is now retired. Charlie tells Harry that half the cells in Azkaban are full because of Mad-Eye, and that he has made himself lots of enemies because of this. According to Charlie, Moody has been getting more paranoid in his old age; he doesn't trust anyone, and sees Dark wizards everywhere he goes. The day before the Hogwarts School term begins, there is an incident at Mad-Eye's house, which the Improper Use of Magic Department go to investigate. Moody tells them that he heard an intruder trying to break into his house, before his magical dustbins ambushed them.
Moody enters the Great Hall amid a deafening rumble of thunder, and stands in the doorway. He is shrouded in a black travelling cloak, and leans upon a long staff. A flash of lightening illuminates Moody in the doorway; he lowers his hood, revealing a long mane of grizzled, dark grey hair. When Moody walks up towards the staff table, a dull clunk echoes throughout the Great Hall. A further flash of lightning illuminates his face; it looks as though it has been carved out of weathered wood by someone who had only a vague idea of what a human face looks like. Every inch of his face appears to be scarred, a large chunk of his nose is missing and his mouth looks like a diagonal gash. One of Moody's eyes is small, dark and beady; the other is large, as round as a coin, and is a vivid, electric blue. The blue eye moves constantly, without blinking, and rolls around quite independently of the normal eye. It rolls right over for a moment, pointing into the back of Moody's head, revealing only whiteness to the assembled students.
Moody stretches out a scarred hand to Dumbledore when he reaches the Headmaster, and the pair shake hands. Moody shakes his head unsmiliingly when Dumbledore asks him a question, and replies in an undertone. He sits in the empty seat next to Dumbledore and pulls a plate of sausages towards him. Raising the plate to his nose, he sniffs the sausages suspiciously. Taking a small knife out of his pocket, he spears the sausage and begins to eat. As he does, his normal eye is fixed upon the food; the blue eye darts restlessly around in its socket, taking in the Hall and the students.
Dumbledore reveals that Moody is the new Defence Against the Dark Arts teacher. Moody seems totally indifferent to the lukewarm reception he receives. He reaches into his travelling cloak and pulls out a hip-flask and takes a long drink from it. When he lifts his arm to drink his cloak is pulled a few inches from the ground, revealing several inches of carved wooden leg, ending in a clawed foot.
Professor Moody limps down the marble staircase after Draco Malfoy attempts to curse Harry. He Transfigures Draco into a small, white ferret as a punishment and, pointing his wand at the creature, makes it bounce up and down in the air as he reprimands the student. He tells the students that he doesn't like people who attack whilst their opponent's back is turned, and thinks it is a cowardly thing to do. Moody is calm as Professor McGonagall confronts him, and is unconcerned when she tells him that they do not use Transfiguration as a punishment at Hogwarts. He thought a good, sharp shock would send the message to Draco more quickly. Moody is unfazed when Draco threatens to tell his father about Moody's punishment, and asks Draco to tell his father that Moody is keeping an eye on him. He marches Draco towards the dungeons in search of Professor Snape, the Slytherin Head of house
Moody enters the classroom for the fourth-year Defence Against the Dark Arts lesson. He tells the students they can put away their books, as they won't be needing them. Moody tells the class that they are very behind on dealing with curses, and says that he will be bringing them up to scratch on what harm wizards can do to each other. He tells the class that he has one year to teach them how to deal with Dark magic as he intends to return to his retirement at the end of the year.
Moody asks the class whether they know the three curses that are most heavily punished by wizarding law. He produces a jar containing thre spiders, and proceeds to perform the Imperius Curse, the Cruciatus Curse and the Killing Curse on the spiders during the lesson in turn. Moody is prevented from torturing the spider with the Cruciatius for too long by Hermione, who notices that Neville is badly affected by the sight of the tortured spider. After the lesson, Moody comes across Harry, Ron, Hermione and Neville in the corridor outside the classroom. He maintains that it is important for them to know about the curses, harsh though it may seem. He invites Neville to have a cup of tea with him, and steers the frightened boy away towards his office.
Professor Moody informs the fourth-years students that he will be placing them under the Imperius Curse during their lesson, to demonstrate its power and to see whether they can resist its effects. When Hermione questions the legality of this, Moody tells her that Dumbledore requested they be taught what the curse feels like, and says that she can be excused from the class if she wants. Moody places the Imperius Curse on the students in turn, making them do some extraordinary things. When he comes to Harry, Moody attempts to force him to jump onto the desk. He is impressed when Harry manages to fight the curse, and insists on putting the boy through his paces four more times, until Harry can throw the curse off entirely.
After the feast to welcome the Beauxbatons and Durmstrang delegates Moody walks up to the doors of the Great Hall towards Harry, Ron, Hermione and Professor Karkaroff. He stands there, leaning heavily on his staff, his magical eye fixed on the Durmstrang Headmaster. He tells Karkaroff that unless he has anything to say to Harry, whom Karkaroff had been staring at, he might want to move, as he is blocking the doorway. He watches Karkaroff leave the Great Hall with a look of intense dislike upon his mutliated face, his magical eye fixed on Karkaroff's back.
Moody enters the room off the Great Hall in the middle of the discussion about what to do about Harry. He tells those assembled that Harry has to compete in the Tournament, and thinks it is very convenient. He explains his phrasing, and tells them that he thinks someone put Harry's name in the Goblet on purpose, knowing that he would have to compete if it came out. He thinks someone is trying to harm Harry, and possibly wants Harry to die whilst competing, knowing how dangerous the competition is.
Moody was the Auror who caught Igor Karkaroff and sent him to Azkaban, the wizarding prison. Sirius Black tells Harry that Moody was the best Auror the Ministry of Magic ever had, and that just because he hears intruders a bit too often doesn't mean he can't still spot the real thing.
Professor Moody emerges from a classroom near to the Charms corridor just after Harry tells Cedric about the dragons. He tells Harry to come to his office, and closes the door behind them. He watches Harry closely as the boy looks around his office, and tells him about the Dark Detectors he keeps in there. Moody tells Harry that he doesn't want to play favourites but that he wants to give Harry some general advice. He encourages Harry to play to his strengths, reminding Harry that he is an excellent flier. He gives one other piece of advice to Harry: he needs to use a nice, simple spell to get what he needs. Moody doesn't directly tell Harry anything, but he encourages him to put the two pieces of advice together to figure out what he needs for the first task.
Moody stands with Professor McGonagall and Hagrid as Harry flies back to the ground after the first task. He looks very pleased at Harry's success, and his magical eye dances in its socket as he congratulates Harry.
Moody arrives at the foot of the stairs as Professor Snape and Filch stand arguing. He is intrigued when Filch mentions that Snape's office has been broken into, and wonders who would want to break into it. Moody has already searched Snape's office thoroughly due to his role as an Auror, and found nothing of interest. When Snape challenges him, Moody says that whilst Dumbledore may believe in second chances, he himself knows that some spots don't ever come off. He places a peculiar emphasis on the words as he speaks to Snape, prompting a strange reaction from the Potions teacher. Moody is aware that Harry is on the staircase, as his magical eye is able to see through the Invisibility Cloak. Although he is made aware that the golden egg belongs to Harry, Moody inadvertently draws Snape's attention to the boy after pointing out the discarded Marauder's Map on the stairs. Moody tells Snape that nobody is there when the teacher begins to search blindly for Harry, and finds it interesting how quickly Snape's mind turned to Harry.
After Filch and Snape leave, Moody climbs the stairs to where Harry is hidden. He is curious about the Marauder's Map, and is interested to see how it works. Moody asks whether Harry saw who broke into Snape's office, and is surprised when Harry admits he saw Barty Crouch on the Map. Moody tells Harry that there have been some funny rumours around lately surrounding the Quidditch World Cup, and the appearance of the Dark Mark, and says that if there is one thing he hates, it is a Death Eater who walked free. He asks Harry if he can borrow the Marauder's Map, thinking that he can make good use of the map.
According to Sirius, Moody never killed anyone if he could help it during the first wizarding war, always bringing people in alive where possible. He was tough, but he never stooped to the level of the Death Eaters.
Moody arrives in the Forbidden Forest soon after Professor Dumbledore and Harry in the wake of Mr Crouch's appearance. He blames his leg for not being able to get there quicker, having been told by Professor Snape that something has happened to Mr Crouch. He limps off into the Forest to try and find Crouch.
During one of Dumbledore's Pensieve memories, it is revealed that the missing chunk of Moody's nose was removed during a struggle between the Auror and Death Eater Evan Rosier. Moody was instrumental in the capture of Igor Karkaroff. It took him six months to track the Death Eater down, and he is disgusted at the idea that Karkaroff will be set free if he reveals enough new names of Death Eaters.
It is revealed in Moody's office that the real Alastor Moody has been held captive throughout the school year by Barty Crouch Junior, imprisoned inside his own trunk. He was kept close to the impostor to allow him to create regular batches of Polyjuice Potion, for which Moody's hair was required. The fact that Moody is well known for only drinking from his own hip-flask was one of the reasons the deception worked so well. Crouch Junior revealed that the day Arthur Weasley was summoned to help with a commotion at Moody's house was the day they made the switch. The real Moody was subdued by Wormtail and Barty Crouch Junior, and was forced into his own trunk after some of his hair was taken for the Polyjuice Potion. Under the Imperius Curse, Moody was questioned by Barty Crouch Junior about his past and his habits, to allow the impostor to fool even Dumbledore.
The real Alastor Moody sits at the staff table during the Leaving Feast, his wooden leg and magical eye back in place. Understandably, he is extremely twitchy, and jumps every time someone speaks to him. His fear of attack has clearly been increased by his ten-month imprisonment in his own trunk.
Moody tells Harry not to ask questions until they are inside number twelve, Grimmauld Place, and sets fire to the piece of parchment in Harry's hand. When number twelve, Grimmauld Place magically appears, Moody prods Harry in the back to make him walk up the steps to the front door. Before entering the house, he stands on the top step and releases the balls of light the Put-Outer stole from the streetlamps, then limps inside and shuts the front door. He removes the Disillusionment Charm from Harry, rapping him over the head with his wand, and lights the gas lamps that line the hallway of the house. Once they have entered number twelve, the members of the Order of the Phoenix are directed to a room off the hall by Mrs Weasley, where a meeting has just begun.
Moody enters the Death Chamber with Sirius, Remus, Tonks and Kingsley. They rain spells down on the Death Eaters, hurrying down the stone steps towards the sunken floor of the room. Moody is hit with a spell by one of the Death Eaters; he lies on his side, bleeding from the head, his magical eye spinning away across the floor.
Moody orchestrates the decoy strategy to allow Harry to leave number four, Privet Drive undetected. He tells Harry that seven Harry Potters will be travelling that night, each headed to a different safe house. He produces Polyjuice Potion, sets of clothes, and fake luggage and owls for the decoy Harrys. Moody travels with Mundungus, as he doesn't trust the wizard.