Sandor is the younger brother of Ser Gregor Clegane, nicknamed 'the Mountain', a monstrously huge knight and arguably the most feared man in Westeros.

Sandor Clegane is a skilled warrior in the service of House Lannister, known primarily for the horrible facial scarring he bears on the right side of his face and for his fierce demeanor and lack of chivalry. Following their victory, Sandor returned to a decimated King's Landing, where he died throwing himself from the Red Keep, alongside Gregor, ending their bitter lifelong rivalry and fulfilling his campaign of revenge. Upon the return of the White Walkers and the army of the dead, Sandor fought alongside the armies of Jon Snow and Daenerys Targaryen in order to prevent a second Long Night. After traveling as a fugitive with Arya Stark, having a close brush with death following an altercation with Brienne of Tarth, and the mass murder of a congregation he attempted to find peace with, he reluctantly joined the Brotherhood Without Banners in hopes of having a greater purpose. When Joffrey ascended the Iron Throne, Sandor was named into his Kingsguard (despite not being a knight), but deserted his post at the Battle of the Blackwater. Sandor Clegane, popularly known as the Hound, was the younger brother of Ser Gregor Clegane and the personal bodyguard of Prince Joffrey Baratheon.

You don't know the things I've done.' ―Sandor Clegane to Ray

Why does the hound hate bronn