Aragog died of an unknown illness which he contracted in the summer before the events of Harry Potter and the Half-Blood Prince. Aragog is an Acromantual, an unfathomably huge spider, who lives in the Forbidden Forest and had been Rubeus Hagrid's pet when he was a student at Hogwarts. In fact, Aragog played a role in getting Hagrid expelled from Hogwarts, because Tom Riddle convinced teachers that it was Aragog rather than the basilisk who was attacking Hogwarts students.

Harry and Ron have less-than-fond memories of Aragog, having gone to see him to ask for information at Hagrid's behest in Harry Potter and the Chamber of Secrets. While Hagrid had assumed that the courtesy Aragog showed him by not allowing his family members to eat him would be extended to his friends, it was not, and Harry and Ron would have been killed had they not been rescued by Mr. Weasley's runaway Ford Anglia.

After his death, Hagrid managed, with great difficulty, to extract Aragog's corpse from the Forbidden Forest and arrange him a burial, which was attended by Harry and Horace Slughorn. It was thanks, inadvertently, to Aragog's death that Harry was able to extract from Professor Slughorn the much-needed memory that confirmed to Dumbledore the existence of Lord Voldemort's horcruxes.