Summer

Summer is one of six direwolf cubs found by the children of House Stark. Summer is adopted and raised by Bran Stark.

Season 1
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.

Season 2
Summer is kept inside the godswood of Winterfell. Bran is experiencing Summer's actions and movements in his dreams. After Theon has taken Winterfell, Summer is seen fleeing through the Godswood with Osha, Bran, Rickon, Hodor and Shaggydog.

Season 3
Summer follows Bran on his journey North. Bran's group are encountered by Jojen and Meera Reed, Meera places a knife to Osha's throat, causing Summer to get angry, but Jojen calms him down. Later, Bran possesses Summer and uses him to kill a wildling while hiding from them in a nearby tower. After encountering Samwell Tarly (after he compares Summer to Jon Snow's direwolf Ghost), Summer continues following Bran beyond the Wall.

In the books
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"