A direwolf is an unusually large and intelligent species of wolf. A grey direwolf on a white field is the family symbol and crest of House Stark.
Grey Wind is arguably the most disciplined of the six cubs; he follows Robb’s commands almost to the letter. Grey Wind was adopted and raised by Robb Stark.
Ghost is the quietest and stealthiest of the six wolf cubs. Whilst the other wolves are darker-colored, Ghost is an albino and initially appears to be the runt of the litter, though he grows up to be as big as any of the others. Ghost was adopted and raised by Jon Snow.
Lady is arguably the gentlest and most trusting of the six wolf cubs. Lady was adopted and raised by Sansa Stark.
Nymeria is an exuberant and playful wolf, but is also fiercely defensive of Arya Stark. Arya names Nymeria for the warrior-queen of the Rhoynar. Nymeria was adopted and raised by Arya Stark
Summer is fiercely defensive of Bran, but is arguably the most playful of the six cubs. Summer was adopted and raised by Bran Stark.
Shaggydog is the fiercest and least-disciplined of the six wolves, reflecting Rickon’s willful nature. Shaggydog was adopted and raised by Rickon Stark.
Source: http://gameofthrones.wikia.com
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