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Sandor was basically a good man and he was obeying Joffrey only because he was bound by duty.
Sandor had a past with fire. In one of the episodes from Season 1, we learn that when Sandor was a kid, his elder brother Gregor (“the Mountain”) shoved his face into brazier over a trivial incident, resulting in Sandors horrific scars.
During the Battle of the Blackwater, he initially comports himself bravely, but the fire really shakes him. Its possible his memories of childhood flooded back, which is why he became disillusioned in regards to knighthood and duty. (He often speaks of his disdain for knights and their supposed nobility, citing his monstrous brother as an example. Sandor never accepts knighthood for this reason.)
The combination of his personal dread, and the realization that hes facing death by fire for King he does not love or respect (Joffreys treatment of Sansa, who Sandor has great sympathy for is a major factor), led Sandor to abandon his post and his king. Thats why he turns back, gets drunk, and abandons Kings Landing.
We learn how Sandor “The Hound” Clegane was first disfigured during S01E04 at a tournament held for Ned Stark becoming Hand of the King:
[Video Link was dead, but transcribing remains… Huzzah!]
At the Battle of the Blackwater (as you mention S02E09) The Hound is confronted by a soldier who is completely on fire. This causes The Hound to freeze up and not dispatch his burning attacker and is only saved when Bronn shoots the solider with an arrow (scene below).
The Hound becomes disengaged in the battle after this encounter and retreats back through the gates when he and Tyrion exchange some words (same scene as above).
I do not think it was Joffreys attitude that caused Sandor to leave as Joffrey never treated Sandor well (always calling him “dog”, speaking to him a derogatory manner, etc.) Sandor flashed back to his childhood and realized that if he was going to die, it sure as hell wasnt going to by burning to death. He almost admits as much to Sansa after he leaves the battle and goes to her chambers (scene below).
This ends up being a recurring theme. See his reaction during the duel with Beric Dondarrion (S03E04) and being asked to look into the flames by Thoros of Myr (S07E01).
The characters of Sandor Clegane and Gregor Clegane, or The Hound and The Mountain, respectively, appear at first blush to be quite similar, but later turn out to be foils of one another. While The Hound is loyal above all else, The Mountain is pure violence and evil. He makes Ramsay Bolton look halfway sympathetic. The Hound has killed many times, but always at the orders of the person he serves. He killed the butchers boy, true, but only under Joffreys orders. When he was helping Arya, he stopped at nothing to protect her. The Mountain, on the other hand, is famed in Westeros as an indiscriminate murderer and rapist. Much like Ramsay, Gregor Clegane is purely evil.
The brothers hatred of one another goes deeper than Sandors first hand experience of Gregors cruelty. They are constantly at odds because they are one anothers intellectual and spiritual opposite, yet they are deeply connected by blood. Season 6 of Game of Thrones has dealt with resurrection and the impermanence of death quite a bit. The Wights and White Walkers, Jon Snow, and The Mountain himself have all been resurrected from the dead. The Hounds return, after he was presumed dead, would fit nicely into the theme of this season.
Fans are already gearing up for a highly anticipated showdown between The Hound and The Mountain, referred to in forums across the internet as “Cleganebowl.” So far, it is just a theory, but the possible return of The Hound could mean that its true. The theory goes that The Hound and The Mountain will have to fight to the death in Cersei Lannisters trial-by-combat. You may recall Cersei mentioning her upcoming trial in Episode 6. She wasnt worried because, of course, her champion will be The Mountain. But maybe fans are right, and The Hound is about to fight his brother. In which case, Id tell Cersei to be worried. More Like This
If the rumors are to be believed, Episode 7 of Game of Thrones might see the return of one thought-to-be-dead character, Sandor Clegane, otherwise known as The Hound. You may remember The Hound as Joffreys (aka The Worst) head henchman with an apparent soft-spot for Stark daughters. He saved Sansa from a violent molestation, and protected Arya as she journeyed away from Kings Landing after her fathers beheading. While The Hound can be vicious, his brother Gregor Clegane is a whole other ballgame in terms of evil, and the two do not get along. Why do the brothers Clegane hate each other so much? Well, it started with some childhood squabbling, in which Gregor once shoved Sandors face into a fire, which would put anybody off.
A Storm of Swords
Sandor is captured as a drunken vagabond by the Mad Huntsman, at Stoney Sept in the Riverlands. Hes claimed by the Huntsmans companions of the Brotherhood without Banners, who also had Arya stark in their custody. Days later they arrive at the hollow hill, there Sandor is put on trial for the various attrocities commited by the Mountains Men of House Clegane, but no specific crime could be attributed to him, until Arya told the Brotherhood about his murder of her friend Mycah. Since the court lacked evidence, the Brotherhoods leader; Lord Beric Dondarrion, decreed that the matter would be settled in trial by combat. Beric fought with a magically enchanted flaming sword, and despite a severe hangover and his crippling fear of fire, Sandor won the duel and his life. The Brotherhood stripped him of his money and possessions, save for his weapons and raging horse, and sent him on his way, but Sandor soon returned with the intention of reclaiming his possessions by force. He reveals himself to the Brotherhood in a destroyed village, after the outlaws defeated a band of Brave Companions, and threatens to kill them but he fails to scare them. He refuses to leave and keeps following the Brotherhood, until he came accross Arya, escaping the outlaws because they are taking too long to bring her to her family, and captures her, hoping to ransom her to her brother, Robb, at the Twins, during the wedding of Lord Edmure Tully and Roslin Frey.
During their travel to the Twins, Sandor and Arya have an aggressive relationship. Sandor scares Arya and commands her to keep her mouth shut. The first days she makes fierce resistance which always results with the Hound hitting her. Since she tries to kill him with a heavy rock, Sandor rolls Arya in his horse blanket and ties her every night. After Arya mentions Mycahs death once again, the annoyed Sandor grabs her and warns her to never mention the boy again or he will beat her bloody. The journey to the Trident is unpleasant as it keeps raining for days that even Robbs host marches slowly to the Twins. Initially, Arya writes her name on the trees for the Brotherhood, until shes caught and punished by the Hound, so she can only hope that Thoros will find her in his flames. Arya catches a fever and keeps coughing and sneezing in the rain, but she doesnt dare to speak to Sandor anymore or else he will beat her. At some point shes so weak and soaked that she tells Sandor that shes feeling bad, but he only tells her to to shut her mouth. When Sandor and Arya reach Lord Arroways Town they find it flooded and deserted. Sandor promises to pay some ferrymen to take them across the Trident. Arya gives up the idea of jumping off the boat after one of the men falls into the raging river. When they reach their destination, Sandor gives the men only the parchment Lord Beric had given him promising reimbursement after the war.
Sandor finally sees that Aryas fever is getting worse, so he gives her more food and lets her to talk, telling her that he once saved Sansa from rape and murder and that she sang a song for him during the Battle of the Blackwater. He reminds the girl that hes not as bad as his brother, who would have spared Arya only if she told him her identity, then thrown her to Cerseis feet. When Arya tells him that she was Gregors captive and that she wishes to kill him and some of the Mountains men, Sandor is impressed that she knows the names of Dunsen, Polliver, Raff the Sweetling, and the Tickler, himself being familiar with Gregors band. Arya wonders why Sandor hates his brother so much that he wants to kill him. Sandor finally reveals that hes not working for the Lannisters anymore and hes not taking her back to Joffrey and the queen, but to the Twins, hoping to get a lordship from Robb and maybe enter in the Starkss service if Robb doesnt mind having a Clegane. When Arya states that Robb will never take Sandor at his service, Sandor says that he will just take money and laugh at Robbs face. Then he insults Arya again and commands her to keep silent once again.
Later, Sandor takes a wagon of food for the wedding feast from a man, he scares some farmers and takes food from them as well as a pair of boots, telling them to be thankful that hes not taking anything else. Like Yoren, he cuts Aryas hair again, doing the job so badly that her hair became a complete mess and her dirty appearance make her impossible to be recognized by her own family, though shes glad about that due to her fear of Roose Bolton meeting her before she can find her brother or her mother.
Fortunately for their lives, Sandor arrived at the Twins just as Robb Stark was being betrayed and slaughtered by the Freys. He is sent to the camps by Ser Donnel Haigh and then sent away by Bolton men-at-arms. When the massacre occurs, the tents outside are set afire and the Freys destroy Robbs army with catapults and soldiers. Sandor and his brutal horse Stranger fight against 3 Freys, resulting with the deaths of Ser Tytos Frey and Ser Garse Goodbrook. Realizing that her family is likely dead in the castle, Arya flees because she doesnt want to stay with Sandor. But he manages to catch her back by throwing an axe on her head, and kills a few soldiers on his way out of the battlefield.
Clegane is more angered than usual due to his failed ransom. He took Arya with him and the day after the massacre the two find a cowardly young mare who fled from the Twins, Arya names her Craven and rides her. She has to feed both horses as well as waking up when Sandor wants it. If she doesnt Sandor uses bad manners to get her up, like throwing cold water on her or screaming insults. Sandor has lost interest in keeping her under control, leaving her free at night, so Arya wishes to kill him but she never does. She doesnt know her grandfathers brother, Ser Brynden Tully, and she thinks he might refuse to let her in Riverrun, so she considers riding in search for Acorn Hall and return to Lady Smallwood but she could never find the castle again. She considers trying to find Sharnas inn where Hot Pie works, or the Brotherhood without Banners, but she changes her mind because she would only get lost in the wilderness, Gendry and Hot Pie abandoned her, and Beric only wanted to ransom her, and since no one wants her she decides she will stay with Sandor.
Sandor and Arya avoid any town, castle, and village around. Now that the northern rebellion is over, the royal armies ride throughout the riverlands to restore the kings peace and bend the defying river lords or killing Brave Companions. Whole days pass when neither of the two say a word, Arya being too depressed and Sandor being full of cold fury. He does everything with anger and insults Arya all the time, causing her to hate him even more for the unfair treatment since she behaved like a good captive, yet Sandor calls her whiny and complains how he should hand her over to the Silent Sisters. They often have to hide as they see columns of horsemen with the Frey banners, hunting for running northmen. As the two keep travelling, Joffrey Baratheon dies at his wedding feast at Kings Landing.
One day they find a dying man of House Piper, whos a victim from the Red Wedding and Robbs s follower, with a wound full of blood and pus. The soldier was serving under Ser Marq Piper, whos now a captive at the Twins. He was wounded with a mace by a Bolton man and has a broken shoulder with his own chainmail in his flesh. He begs Sandor for a drink and the gift of mercy, and recognizes him as Joffreys dog. Sandor replies that hes now free and gives him water, both soldier and Sandor wishing it was wine. The man gets the mercy of death by Sandor who shows Arya where the heart is. He takes the soldiers money and gives Arya the mans dagger and helm.
The two head towards the Vale of Arryn, and they stop in a village in the Mountains of the Moon, for a short time. They work there, until they are forced to leave since the inhabitants are feeling uncomfortable with their presence. Sandor decided to change course and find another of her relatives to ransom her to, first choosing to bring her to her aunt, Lysa Arryn, at the Eyrie.
The Hound and Arya keep travelling to the Eyrie until they learn of the Vale mountain clansmen being now heavily armed, thanks to Lord Tywin Lannisters rewards. Since Lysa is deliberately avoiding to stop them since Jon Arryns death, its almost impossible to travel to the Mountains of the Moon without being attacked. Sandor heads back to the Riverlands with the intention to bring Arya to Ser Brynden Tully. However Riverrun is under siege by the Frey army led by Ser Ryman Frey, with the support of the Lannister army led by Ser Daven Lannister. Sandor is unable to get rid of Arya, while the two have often quarrels, but also started to get along after the Red Wedding. The two share a common nihilistic view of the world and agree on many things. Arya decides to remove the Hounds name from her list, since he saved her from turning into a Frey captive or being killed by their soldiers.
With Riverrun and the Eyrie inaccessible, the prospect of ransom grows dimmer and dimmer, as the two travel the Riverlands. They come accross the Inn at the Crossroads and they are accosted by some of the Mountains men, with whom Arya holds a grudge. The Tickler tells Sandor about the marriage between Tyrion and Sansa, about Joffreys death, Tyrions arrest, Sansas disappearance, and Harrenhal being under control of House Clegane, while Gregor is in Kings Landing for his trial by combat. When Polliver and the Tickler try to bring Sandor to Harrenhal, a fight breaks out, and despite severe hunger and drunkeness, Sandor and Arya manage to kill them. Sandor personally slains Polliver, while Arya repeatedly stabs the Tickler. Sandor agrees to give the mercy of a quick death to a squire of House Sarsfield and shows Arya where the heart is. The two escape from the lands, since Gregor is holding them, and ride back to the lands not far from the mountains of the Vale.
Sandor suffered a wound to his leg from his previous fight, and despite Aryas best efforts, it grew infected. The next day Sandor eventually collapses underneath a tree, and begs Arya for a swift death. He tries to get Arya killing him by reminding her about how he was Joffrey and Cerseis minion; he also shows both anger and pain at Tyrion being married to the now missing Sansa, and regrets not having killed him back at the Blackwater. He tries to get Arya finish him by telling how he should have fucked Sansa bloody and ripped her heart out instead of leaving her with the dwarf. Arya still refuses him however, and leaves him to die in pain as a revenge for murdering her friend and for any other innocent he killed.
Some days later, Arya arrives at the town of Saltpans only to find it burned and almost completely destroyed, except for the keep of House Cox. A group of criminals savagely raped, mutilated, and murdered most of the men, women, and children of the place, leaving only a few to rebuild the town and bury the corpses. Arya finds there a boat for Braavos.