The Impersonation of Mad-Eye Moody
Alastor 'Mad-Eye' Moody managed to alter the Triwizard Tournament in Harry Potter and the Goblet of Fire as the one who put Harry's name in the Goblet of Fire, but it took a well-orchestrated plan. Although Mad-Eye served as a key member for the remainder of the Harry Potter franchise, he wasn't exactly himself in his introductory appearance. In fact, another figure was impersonating him all along. Albus Dumbledore hired the wizard as the new Defense Against the Dark Arts professor. During his only year as the DADA professor, he guided Harry Potter during the Triwizard Tournament but had ulterior motives.
David Tennant as Barty Crouch Jr in Harry Potter and the Goblet of Fire
Lord Voldemort needed a pathway for Harry to complete a ritual that would bring back the Dark wizard's physical body, and that opportunity hinged on the student's participation in the Triwizard Tournament, leading to who put Harry's name in the Goblet of Fire. To infiltrate Hogwarts to manipulate Harry, Voldemort enlists the help of a Death Eater named Barty Crouch Jr., who previously escaped from Azkaban. Barty then kidnaps Mad-Eye and disguises himself as the professor by using a Polyjuice Potion. This allows Barty to walk freely around Hogwarts as he concocts a precise plan to give Harry a chance to participate in the Triwizard Tournament.
Barty Crouch Jr. conjuring the dark mark at the World Cup in Harry Potter and the Goblet of Fire
The Goblet Of Fire Was Confused By A Confundus Charm. The Triwizard Tournament traditionally features one student from each of the three schools in attendance. That trio of Champions has to be 17 based on the age spell Dumbledore put in place. Despite those restrictions, Harry's name was chosen as the fourth Champion, prompting people to wonder who put Harry's name in the Goblet of Fire, the impartial judge used to select contestants. While staff and fellow students believe Harry put his name in the Goblet of Fire, it was Barty Crouch Jr. disguised as Professor Moody. Barty uses a Confundus Charm to confuse the Goblet of Fire, so it selects Harry's name as the fourth contestant from an unspecified school.
Harry Potter & Voldemort in Goblet of Fire.
The Misconception of Harry's Involvement
There is a Goblet of Fire scene in which Dumbledore basically pins Harry against a wall and asks him roughly, 'Harry, did you put your name in the Goblet of Fire?' The scene occurs directly after Harry's name flies out of the Goblet, and Dumbledore calls him out in front of the entire Great Hall. He takes Harry back with the rest of the champions, as well as their respective school's headmasters, and starts to immediately grill Harry about how and why exactly his name was selected.
Dumbledore talking to Harry Potter in Harry Potter and the Goblet of fire
Unfortunately, many believe Harry put his name in the Goblet of Fire because they think his ego has gotten the better of him. Many believe Harry wants the glory of winning the Triwizard Tournament all to himself, including, for a brief moment, Dumbledore. There is no question Harry has a reckless streak while attending Hogwarts, but many think this is due to him having something to prove. Fortunately, the question of who put Harry's name in the Goblet of Fire is found not to be Harry, as Dumbledore recognizes that only dark magic could've confounded the Goblet, and Harry isn't capable of that.
Amos Diggory and Dumbledore in Harry Potter and the Goblet of Fire
The Fate of Barty Crouch Jr.
Many characters, such as Bellatrix Lestrange and Sirius Black, escaped from the Dementors in the wizard prison Azkaban. However, in the end, Barty Crouch Jr. isn't able to outrun the Dementors once he's caught the second time around. The Harry Potter and the Goblet of Fire ending doesn't explain what happens to Barty Crouch Jr. after he's exposed for impersonating Mad-Eye Moody. Rather, he's simply carted out of the room and is never heard from again. It's implied he's taken back to Azkaban, but this would create an Order of the Phoenix plot hole – there's a mass breakout at the beginning of the film, but Barty Crouch Jr. isn't there.
Voldemort and Wormtail standing in the graveyard in Harry Potter and the Goblet of Fire
While the movie offers zero explanation, the books explain what happened to Crouch Jr. In J.K. Rowling's novels, it's said that Crouch is taken to the Dementors to suffer the Dementor's Kiss, which sucks the soul out of his body. It's a fitting end for the Harry Potter character, as taking him back to Azkaban would've not only created a plot hole but would've proved an unworthy punishment for someone who has already broken out once before.
Tom Felton as Draco Malfoy Scared and Angry in Harry Potter and the Goblet of Fire