Dobby

"You shall not harm Harry Potter!" — Dobby standing up to his former master, Lucius Malfoy.

Dobby is a House-Elf who has had a history with Death Eaters. He warned Harry not to go to Hogwarts', as Lord Voldemort planned to open the Chamber of Secrets.

Chamber
Dobby appears in Harry Potter's new bedroom throwing his schoolbooks in the bin. He tells Harry not to go back to Hogwarts', but Harry argues. Dobby angrily starts humping the drawers as it is Elf mating season, to Harry's disgust, and then runs off into the kitchen. He bewitches a cake to hover into the living room and collide with Mrs Mason's face before vanishing instantly.

He appears once more where he blocks the gateway at Platform Nine-and-Three-Quarters, making sure that Harry and Ron cannot go aboard the Hogwarts' Express. Dobby is also the one responsible for cursing a Bludger which attacks Harry in a game of Quidditch. Ron and Hermione confront Dobby and defeat him, eventually knocking him unconscious.

After Lord Voldemort's soul is destroyed and the Basilisk is killed, Dobby is revealed to be the slave of Lucius Malfoy, who pays Dobby by giving him female Elves to mate with. Lucius can control and torture Dobby at will. However, when Harry gives him a sock, Dobby is set free. Lucius attempts to kill Harry, but Dobby disarms him and turns his pants into a magenta thong, claiming it to belong to Lucius's wife.

Prisoner
Dobby decides to work at Hogwarts' as a chef. He makes the feasts for the students, as he likes to work and there are plenty of female Elves there. However, he realises that he needs money as payment, instead of female Elves, and figures out that he's poor. However, when he confronts his boggart, it turns into Lord Voldemort. Dobby, thinking fast and furiously, turns Lord Voldemort into an infant and sends him to Wormtail in exchange for 50 Galleons.