Male Acromantula, an enormous sentient spider. Hagrid raised him from an egg as a Hogwarts student, supposedly keeping him inside a cupboard. The spider's discovery was partly responsible for Hagrid's expulsion.
While Aragog started as Hagrid's pet, after the expulsion he lived in the Forbidden Forest. Hagrid even found him a wife, Mosag, with whom Aragog had many offspring and became the patriarch of an entire colony of Acromantulas. He remained grateful to Hagrid, and kept his carnivorous children from attacking him when he came to visit (the service didn't extend to anyone else, as Harry, Ron and Fang found out the hard way in Chamber of Secrets). Aragog remained in the forest for the rest of his long life, eventually growing weak, going blind, and dying of natural causes after an illness in Half-Blood Prince.
He/she died at the age of 55 in 1997.
Individual Additional Information
Relationships
Aragog had an unspecified social relationship with Rubeus Hagrid.
Aragog 
