The subject of this article originates from non-canonical sources. To find out about what is considered "canon" see LOTR:Canon.
The Dire wolves were a large pack of wolves that served under the Witch-king of Angmar. They assisted him in retaking Angmar from the Black Númenóreans. They were all killed in this battle, though more came to the Witch-king later. Dire wolves were present at nearly every battle in the Angmar War. The wolves were possibly sentient. Dire Wolves are not considered canon, as they only appear in the video games. In Rise of the Witch-king, they can be upgraded with Banner Carrier and Spiked Collars.
An extinct animal of the same name existed in the real world - "dire" is from the Latin meaning "Fearsome".