Bartemius Crouch Jr., known as Barty, was one of Voldemort’s most faithful Death Eaters. Barty Crouch Jr. was the only child of Ministry official Barty Crouch, Sr., who personally sent his son to Azkanban.
Barty Jr. was among Death Eaters who tortured the Longbottoms, and was caught and sent to Azkaban for the crime in the winter of 1981-82 when he was around 19 years old (OP27). Less than a year later, Barty Crouch Jr. was rescued by his mother who convinced his father to allow her to magically change places with the boy. Barty Sr. quickly realized the extent of Barty’s allegiance to Voldemort, and went to extraordinary lengths to keep his son imprisoned at their home. This worked for over ten years, but Barty Crouch, Sr. was no match for the Dark Lord. Once Voldemort regained his powers, he went looking for his faithful servant.
Voldemort had gained quite a lot of information from his torture of Bertha Jorkins, which he used to create an elaborate plan to circumvent Dumbledore's powerful protections of Harry Potter. Barty Jr.'s part of this plan was to take Polyjuice Potion to impersonate Mad-Eye Moody (an Auror, and the new Defense Against the Dark Arts instructor at Hogwarts), manipulate the Triwizard Tournament so Harry would enter and win, and then turn the Triwizard Cup into a Portkey to carry Harry to Voldemort.
The plan worked, and Voldemort was able to regenerate himself with Harry’s blood, but Harry escaped Voldemort and returned to Hogwarts. Soon Crouch’s disguise was revealed, the real ‘Mad Eye’ Moody was released, and after a dose of Veritaserum, Barty Crouch Jr. told the entire tale. In one of his many blunders, Minister of Magic Cornelius Fudge allowed a Dementor give Crouch the Dementor's Kiss, leaving him worse than dead (June 24, 1995).
Barty Crouch, Jr. seems to have been a person of extraordinary -- if twisted -- intellect. If his father's ravings are correct, Barty earned 12 O.W.L.s (OP28), something even Hermione couldn't do. He also was able to successfully impersonate the powerful Auror 'Mad Eye' Moody for almost 8 months, even though Barty had spent most of his adult life in Azkaban, or Imperiused at his father's house.
Father: Barty Crouch Sr.
Mother: Mrs. Crouch
Grandfather: Bartemius Crouch Sr. had a grandfather who owned an Axminster, a twelve-seater flying carpet that the whole family could ride on. Of course, that was before flying carpets were banned in Britain (GF7).
"crouch" = adopt a position with knees are bent and body bent forward, sometimes to avoid detection
Alohomora! podcast listeners will recall the (somewhat affectionate) nickname given to Barty Crouch Jr. so as to differentiate him from his father during discussions of Goblet of Fire. Alohomora! Host and Mugglenet staffer Laura Riley was particularly fond of the nickname Little Crouch. --Hufflepuffskein
Discussants on Episode 3 of the Mugglenet Academia podcast mentioned that Little Crouch should be considered an Identity Thief, in the modern usage of the term. Further, polyjuice potion as a substance is basically a vehicle for identity theft. --Hufflepuffskein