A DIREWOLF is a close relative of the wolf, but larger and stronger. They are named after the real world direwolves, Pleistocene megafauna, which were larger than modern wolves (but not as large as portrayed in the books). Direwolves are extinct north of the wall, as they are a very large and dangerous predator, and people have probably hunted them out. A grey direwolf in a white field is the sigil of House Stark.
"Me, Richard, Alfie, and Kit, we sort of rule the young ‘uns for being the exact same age and starting at the same time. We took on this adventure together. It’s quite lovely that we’re all still very much in love with each other. And then obviously, my girl Rose Leslie, who is just the coolest chick on the entire planet. I’m determined - determined! - to be a wildling extra at some point, just to find her and kind of say, ‘I’m in Iceland!’, and see what she says. We’re complete geeks, all of us. Of course, each of us thinks we’re the one that’s going to win.” — Emilia Clarke