|Death||April 21, 1997|
|Appearance||large spider; black and grey body; eight milky-white eyes|
|First appearance in canon||Aragog (CS)|
Aragog was a large Acromantula that lived in the Forbidden Forest at Hogwarts (CS15). Rubeus Hagrid raised the spider in a cupboard, and they were friends until the spider's death (HBP22). Out of loyalty to Hagrid, Aragog never harmed a human (CS15).
When the Chamber of Secrets was first opened, Aragog sensed the presence of the Basilisk in the castle, and begged Hagrid to release him; Acromantula are terrified of Basilisks. Despite Rubeus' repeated requests, however, Aragog never revealed the name of the creature.
Tom Marvolo Riddle arranged it so that Hagrid's pet Acromantula would be blamed for the death of Myrtle (CS17). Hagrid protected Aragog and arranged a shelter in the Forest for him. The gamekeeper also found a wife for Aragog, Mosag; the two Acromantula had a large family (CS15).
Hagrid instructed Harry Potter and Ron Weasley to follow the school's fleeing spiders to Aragog's lair in order to help them discover what was hidden in the Chamber of Secrets (CS14); the pair came to the conclusion that whatever was petrifying the students—a Basilisk—was a lethal enemy of arachnids. Despite Harry and Ron's closeness to Hagrid, however, Aragog was not able or willing to prevent his children from attacking the boys. Aragog was fairly old by then, and blind (CS15).
Four years later, Hagrid stated that Aragog was dying, and that it was no longer safe for anyone other than the gamekeeper himself to approach the lair (HBP11). Eventually, the Acromantula died, and Hagrid had to fight to get its body and bring it to the school grounds so he could bury it as Acromantula usually eat their dead.
Harry attended the burial, after drinking some Felix Felicis. He met Horace Slughorn on his way to Hagrid's hut, and the professor went with him, marvelling at the possibility of acquiring some valuable poison from the dead Acromantula. Slughorn succeeded, and later made a grand speech about the friendship of Aragog and Hagrid.
The three wizards sat in the hut and drank to the Acromantula's honour. Taking advantage of this, Harry disturbed Slughorn enough with the thought of Lily Potter's death to coerce the teacher into giving him the memory in which he told Tom Marvolo Riddle about Horcruxes (HBP22).