Question: In many fantasy stories, there are creatures called Dire Wolves. What's a Dire Wolf, how is it different from existing wolves?

Answer: 
[Wikipedia says](http://en.wikipedia.org/wiki/Dire_Wolf) they're not fictional, although some stories may give them supernatural properties. They're an extinct species that existed from the [Early Pleistocene](http://en.wikipedia.org/wiki/Lower_Pleistocene) to [Late Pleistocene](http://en.wikipedia.org/wiki/Late_Pleistocene) stages (roughly between 1.8 million – 10,000 years ago) in North and South America. Dire Wolves were one of many [Pleistocene Megafauna](http://en.wikipedia.org/wiki/Pleistocene_megafauna), which are basically large animals that existed at that time, which included sabre-toothed cats, mammoths, giant lemurs, and giant sloths. Dire Wolves are larger than [gray wolves](http://en.wikipedia.org/wiki/Gray_Wolf) (the largest existing type of wolf), averaging 5 ft in length and 240 lbs, although they tended to have shorter legs proportionally than gray wolves.
Generally, "Dire" animals are larger, more vicious versions of existing animals. They're common in RPGs like D&D and other games or fiction with similar fantasy themes. In D&D (at least in more recent editions), in addition to being larger dire animals also tend to have bony plates and spikes.