Hodor is a simpleminded servant of House Stark at Winterfell working in the stables. He aids Bran Stark's mobility after he sustains a paralyzing injury when falling from a tower by carrying him from place to place, in his arms, in a basket on his back, and in a wheelbarrow. After Winterfell is captured by Theon Greyjoy, Hodor escapes with Osha, Bran, and Rickon leaving a trail, then back tracking to hide in the Stark crypts. When emerging to find Winterfell burned, he leaves with Osha to take Bran and Rickon north to the Wall to Jon Snow.
Hodor is simple-minded (i.e. mentally disabled) and he is only capable of saying one word, "hodor" (which is a nonsense word), though he can apparently understand complex instructions other people give him. Nonetheless, House Stark set him to work at a productive occupation within his capacities, as a stableboy serving at Winterfell. Hodor is incredibly large and strong. While he is slow of wits, he is gentle and loyal to the Starks. He is actually Old Nan's great-grandson and only living relative.
Hodor greets the arrival of King Robert with the rest of the Stark household.
Theon Greyjoy directs Hodor to carry the crippled Bran Stark to the great hall to meet Tyrion . He holds Bran whilst Tyrion offers to give him the plans for a new kind of saddle that he can ride even in his crippled state. Some weeks later, Hodor excitedly bursts into Bran's room with the saddle made from Tyrion's diagram.
Hodor bathes naked in the hot pool in the godswood while Bran prays. Hodor is seen by Osha, who tells Bran that she thinks he must have giants' blood in him. Bran reminds Hodor to get dressed.
Bran dreams that he is Summer, seeing the world through the direwolf’s eyes as he stalks through the Godswood and looks up at the Red Comet. He goes to the pool next to the Heart tree and looks down at his reflection. The next day Bran has Hodor carry him out to the godswood; Osha accompanies them and finds a plant that can be used to make a pain relieving tea. She asks Bran if he has had more strange dreams and he claims that he does not dream at all. He changes the subject to the comet, saying that he has heard men say it is an omen favoring Robb in the War. Osha says that she has heard people say the comet is Lannister red and favors their enemies and that she heard a stableboy say the comet was blood red and marked the death of Eddard. Hodor kneels by the pool and Osha helps Bran to the ground by its edge, affectionately stroking his hair. She tells him that stars do not fall for men and that a red comet signifies dragons. Bran stares at his reflection in the water and asserts that dragons are extinct.
Bran continues to have wolf dreams. During one, he follows Hodor and again sees the world from Summer's point of view. Summer follows Hodor as he comes to wake Bran up. Bran looking through Summer's eyes jumps up on the bed, and Bran finds himself looking down at his own face. Bran wakes to find himself looking into Summer's eyes with Hodor looking on. Bran discusses his dreams with Osha as Hodor prepares his horse. Bran says that he dreamt that the sea came to Winterfell, flooding the castle and killing his people and killing Ser Rodrik Cassel. Ser Rodrik leads the garrison to relieve the siege of Torrhen's Square by an unknown enemy. The attack was a feint orchestrated by Theon Greyjoy who uses the opportunity to seize Winterfell. Later, Osha kills a guard, then leads Hodor, Bran, and Rickon out the gate, freeing them from the clutches of the Ironborn. They travel to a shepherd's farm on the outskirts of the Stark lands. Theon hunts for them with hounds, tracking them to the farm and then losing the scent. He returns to Winterfell with the charred corpses of two boys, claiming that they are Bran and Rickon. He makes no mention of Hodor and Osha.
When Maester Luwin sees Osha taking bread down into the crypts, he looks at the bodies and realizes that they are not Bran and Rickon. Later in the crypts, Osha tells him that after they escaped, they doubled back through a stream to mislead the hounds, and have been hiding in the crypts beneath Winterfell ever since. Realizing the bodies were orphans working at the farm and that Theon killed them so no one would know that Bran and Rickon had escaped him, they determine not to tell Bran as he would blame himself. However, Bran sitting next to a sleeping Hodor and Rickon has heard them.
When the escapees finally emerge from the crypts, Winterfell has been burned and Maester Luwin is badly wounded in the Godswood. He tells them that the children must be taken to the Wall to Jon Snow who will protect them from the invading ironmen and get word to Catelyn and Robb. Later, Hodor is pushing Bran in a wheelbarrow, while Osha carries Rickon, as they head away from Winterfell.
Hodor is on the road to Castle Black, along with Bran, Rickon, Osha and the direwolves, Summer and Shaggydog. Bran continues to dream about chasing the Three-eyed Raven. In his dreams, he also encounters a strange boy, who he later meets while awake. The boy turns out to be Jojen Reed, accompanied by his sister, Meera. Jojen possesses the rare gift of seeing the past and present through his dreams, and is able to speak with Bran through their dreams. Jojen tells Bran that he is a 'warg', someone who can control the minds of animals.
After seeking shelter in a derelict windmill during a rainstorm, the group notice a band of wildlings chasing down an old man. The sounds of thunder terrify Hodor, who shouts out in panic. Fearing discovery, Jojen tells Bran to silence Hodor, who keeps panicking. Bran unintentionally uses his Warg powers to render Hodor unconscious. With the wildlings still outside, Jojen convinces Bran to Warg through Summer and Shaggydog outside, who then maul to death some of the wildlings. While in control of Summer and Shaggydog, Bran saw Jon Snow outside fighting the wildlings. He tells Osha to take Rickon with her to the holdfast of Greatjon Umber, a loyal bannerman of the Starks. Bran bids a tearful Rickon farewell, who leaves with Osha and Shaggydog, while Bran continues northward with Hodor, Summer and the Reed siblings.
Later, the group arrives at the Wall and stay overnight in an abandoned castle. During the night, Samwell Tarly, with Gilly and her child, meet Bran and the Reeds in the castle. Samwell, noticing the gigantic Hodor and Summer, realizes who Bran is and offers to take them to Castle Black. They refuse and Jojen tells Sam that they are going beyond the Wall, as no force in the realm of Westeros could withstand the threat posed by the White Walkers. Sam reluctantly gives them the obsidian blades as well as obsidian arrowheads found north of the Wall, which he earlier used to slay a White Walker. True to his gentle nature, Hodor initially does not want to take the blade offered to him, only taking it when directly told to do so. That night, Bran, the Reeds, Hodor and Summer finally pass beyond the Wall.
Hodor is captured by the mutineers alongside his companions when they scout Craster's Keep and attempt to free Summer and Ghost. While Bran, Jojen, and Meera are taken inside the keep, Hodor is chained up outside and abused by the mutineers. Rast stabs him in the leg with a spear and states that if he was as big as Hodor, he would be "king of the fucking world".
When Locke attempts to kidnap Bran during the Raid on Craster's Keep, Bran wargs into Hodor and ambushes Locke. Using his immense strength, the Bran-controlled Hodor lifts Locke off the ground and snaps his neck. Hodor is visibly disturbed when he regains control of his body. He later escapes with the rest of his companions.
As the group continues to travel north, they finally arrive to the Heart tree from Bran's visions. As they are approaching the tree, the group is soon ambushed by skeletal wights. Bran wargs into Hodor again to fend them off, but there are too many of them. As they are about to be overwhelmed, one of the Children of the Forest saves the group with her magic. Hodor carries Bran into the cave beneath the Heart tree where the wights cannot reach them, and brings him near the Three-eyed raven.
Hodor remains with Bran in the Cave of the three-eyed raven as the young Stark explores his abilities. Bran has a vision of Hodor in his youth, named Wylis, as an articulate and well-liked stablehand. He helps Lyanna Stark from her horse while watching Ned Stark spar with Benjen Stark. Lyanna suggests that Benjen find a new sparring partner with Hodor after Ned leaves for the Eyrie, and gives Hodor fencing tips. Hodor and Benjen almost have a match when Old Nan comes outside and discourages Hodor from learning to fight, since he is a stableboy, though Ned remarks that with his size, Hodor would make a formidable fighter.
Bran later attempts to use Hodor's original name and get him to speak, but gets only "Hodor" in response. Hodor later carried Bran outside the cave to speak with Meera, then brings him back in when it becomes clear Meera doesn't want to talk.
When the White Walkers and thousands of wights attack the cave as a result of Bran's reckless warging, Hodor holds the back exit of the cave to allow Bran and Meera time to escape. Bran inadvertently wargs into Wylis, linking the minds of the present-day Hodor and the young stableboy from the past. This mental trauma causes Wylis to suffer a seizure, during which he hears Meera shouting the phrase "Hold the door!" through Bran and begins repeating it, eventually slurring the sentence together until it becomes "Hodor". Through Bran's warging, young Wylis experiences his own future death, damaging his mind. Hodor keeps holding the door to give Meera time to escape with the still unconscious Bran, sacrificing his life as the wights inflict numerous wounds on him in their attempt to break out of the cave.
A once intelligent stableboy, Hodor served as Bran's primary means of thransport. He could only express himself with the single word, "Hodor", a handicap revealed to have been caused by Bran Stark's lack of control over his powers. Hodor faithfully traveled north with Bran and the Reeds to find the Three-Eyed Raven, ultimately sacrificing himself so that Bran and Meera could escape the Army of the Dead.
Hodor generally seems to have a happy demeanor, overjoyed by basic things like presenting Bran with a new saddle, hearing the echo of his own voice in a well, or greeting one of the Stark direwolves. He is deeply loyal to the Starks, who have treated him very well. Despite his large size and strength, Hodor is a gentle soul who is terrified by violence - even violence done by himself, as he often cowers in fear instead of fighting back against foes who are actually smaller than he is. Even so, his loyalty to the Starks is so great that he continues to follow (or rather, carry) Bran Stark through great dangers.