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.
Summer follows Bran on his journey to the Wall. Bran's group are encountered by Jojen and Meera Reed. When Meera puts a knife to Osha's throat, Summer gets angry but Jojen calms him down. Later, Bran wargs into Summer and uses him to kill some wildlings while he and his companions hide from them in a nearby mill. After encountering Samwell Tarly at the Nightfort, Summer continues following Bran, along with Hodor, Meera and Jojen Reed to the lands beyond the Wall.
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"