Sandor Clegane is the younger brother of Gregor Clegane and a retainer to House Lannister. He is nicknamed "The Hound", as for much of the series he wore a distinctive helm in the shape of a snarling dog's head. He is considered one of the most dangerous and skilled fighters in Westeros. As a child he received gruesome facial burns when his brother pushed his head into a brazier, leading to Sandors hate of his brother and his fear of fire. That his brother became a knight, despite his brutality only getting worse, led to Sandor's resentment and contempt for the hypocrisy of knighthood and the knights of Westeros.

Sandor acted for a time as bodyguard and servant of Joffrey Baratheon, who regularly called him "Dog". He won the Hand's Tourney after saving Loras Tyrell from Gregor's wrath. While drunk off his winnings, Sandor became enamored with Sansa Stark, but also mocked her for her polished manners. Sandor was eventually named to the Kingsguard, despite refusing to become a knight, and in this capacity he was often assigned to watch over Sansa. Despite his loyalty to Joffrey, he frequently defended her from Joffrey's physically abusive efforts at shaming her. The use of wildfire, a substance resembling napalm, during the battle for King's Landing, led him to flee the fighting and desert. Before fleeing, he sought out Sansa Stark and offered to take her along with him. In her panic, Sansa refused, but recognized how afraid the man had been in battle.

As a vagabond, he was arrested by the Brotherhood without Banners, which also had Arya Stark in its custody. The Brotherhood put Sandor on trial for Lannister atrocities. He chose trial by combat and defeated Beric Dondarrion, after which The Brotherhood stripped him of his possessions and set him free. Sandor returned to get his tourney winnings back, but kidnapped Arya Stark instead, with the intention of ransoming her off to one of her relatives. At a roadside inn they met three of Gregor's men and Sandor was seriously injured in the ensuing fight. His wounds infected and Arya abandoned him in the forest.

Sandor's fate becomes uncertain after this point. The head of a nearby monastery claimed to have buried "The Hound" after encountering him dying on the riverside, but it is hinted at the Sandor himself may still be alive and have joined the monastery. Meanwhile Rorge, a particularly nasty criminal, obtained Sandor' helm and assumed his identity during a brutal spree of banditry. This lead to stories that the hound was still alive and terrorizing the riverlands. Rorge was later killed by Brienne of Tarth and the helm was then taken by Lem Lemoncloak, a member of the Brotherhood without Banners.

From "A Song of Ice and Fire" by George R R Martin