Summer followed Bran around wherever he climbed including the tower where Bran became a cripple. After Bran is bedridden, an assassin tries to kill Bran, but Summer saves him by jumping on the assassin and ripping out his throat, killing him.
In the A Song of Ice and Fire novels, Summer is fiercely defensive of Bran, but is arguably the most playful of the five cubs. He is colored silver and smoky grey, with yellow eyes. Bran names him after waking up from his coma and later mentions , ".... he was the smartest of the litter"