Bartemius
"Barty" Crouch, Jr is the son of Bartemius
Crouch, the once-great wizarding politician. Barty Crouch Jr is also
a Death Eater who was captured with the Lestranges, who were responsible
for torturing Frank and Alice Longbottom, parents of Neville Longbottom.
His father, Bartemius Crouch Sr, who headed the Department of Magical
Law Enforcement at the time, sentenced him to life imprisonment in Azkaban.However, Crouch Senior rescued his son as a favour to his dying wife. When they visited him in Azkaban, Mrs Crouch used Polyjuice Potion to switch appearances with her son, enabling him to escape while she remained in his place. When she died, she was buried under his identity. To prevent him from returning to Voldemort's service, Crouch's father controlled him with the Imperius Curse, and he was kept hidden under an invisibility cloak. Crouch was nursed back to health by Winky, the family's house-elf. When Bertha Jorkins discovered the truth, it reached Lord Voldemort and he rescued Crouch and put his father under the Imperius Curse. Crouch then kidnapped Mad-Eye Moody and, using Polyjuice potion, assumed Moody's appearance and position as the new Defense Against the Dark Arts teacher to infiltrate Hogwarts. Crouch appears to be smart enough to realise that he must avoid deviating from behavior that the real Moody would demonstrate. Despite being an imposter, he does a fair job of teaching the students; even student Dean Thomas says that 'Moody' wasn't entirely sane, but the class still learned vast amounts from him.
Crouch Sr escaped and reached Hogwarts to tell Dumbledore about Voldemort's return, but he was exhausted and delirious. He was murdered by his son on the Hogwarts grounds. The revived Triwizard Tournament was held at Hogwarts, and Crouch was tasked with making sure Harry won. When Harry, along with Cedric Diggory, touched the Triwizard Cup, it transported them to a graveyard, via portkey. There, Cedric was killed and Harry's blood was used in a ritual to bring Lord Voldemort back to power. The plan succeeded, but Harry escaped.
When Harry returned to Hogwarts, Crouch, still under disguise, hoped to succeed where his master failed, but he also was unable to kill Harry, his plot foiled by Dumbledore, Snape, and McGonagall. Under the effect of Veritaserum, a powerful truth potion, he recounted his plan to them. Although he was closely guarded so he could later repeat his testimony, Minister of Magic Cornelius Fudge had Crouch's soul sucked out by a Dementor before being brought to trial, which prevented him confirming Voldemort's return. He still lives, but few would dare to identify his present condition as "alive" — having no memories or sense of self.