Hagrid's pets

Hagrid keeps and has kept a variety of pets, including some which the Wizarding community considers impossible to domesticate. They are not always wrong. Rowling has said that Hagrid has little interest in tamer magical creatures because of the lack of a challenge, although he has a cowardly, albeit large dog (boarhound) named Fang. Hagrid's love of dangerous magical creatures is relatively central to the plot of several books of the series. Rubeus Hagrid

Aragog

Aragog is an Acromantula - an enormous, sapient, talking spider that made a unique clicking noise as he moved in search of prey. Hagrid raises him from an egg as a Hogwarts student, keeping him inside a cupboard.Rubeus Hagrid In his third year at Hogwarts, Hagrid is caught talking to Aragog in the dungeons by Tom Riddle. Riddle then alleges that the creature is the "Monster of Slytherin," and that Hagrid, by extension, has opened the Chamber and released it. In fact, the "Monster" is a basilisk which Riddle, the real Heir of Slytherin, has released.Rubeus Hagrid

After Hagrid's expulsion, Aragog lives in the Forbidden Forest. Hagrid even finds him a mate, Mosag, with whom Aragog has many offspring and becomes the patriarch of an entire colony of Acromantulas. He remains grateful to Hagrid and keeps his carnivorous children from attacking him when he comes to visit,Hagrid but this does not extend to anyone else, as Harry, Ron, and Fang found out in Harry Potter and the Chamber of Secrets. Hagrid has told them to simply "follow the spiders." Doing as he wishes, they find Aragog, who reveals clues to the true identity of the Monster of Slytherin. Next, Aragog and his children try to eat Harry, Ron, and Fang, who are only saved at the last minute by Mr Weasley's flying car that has been lost in the forest a few months prior. Aragog remains in the forest for the rest of his life, eventually dying in Half-Blood Prince of old age. Hagrid retrieves Aragog's body from the forest, fearing that his children would devour his body.

Later in Harry Potter and the Deathly Hallows Aragog's offspring return during the Battle at Hogwarts; having been driven from the Forbidden Forest, they begin to attack Death Eaters and Hogwarts' inhabitants indiscriminately. Hagrid endangers himself and, potentially, other Hogwarts' inhabitants by attempting to protect Aragog's offspring from harm, in fact being captured by them and taken to Voldemort.

Aragog was voiced by Julian Glover in the film adaptation of Harry Potter and the Chamber of Secrets.