Better known as the Hound, Sandor Clegane is pretty notable from the start of Game of Thrones. He’s a giant among men, and is the guard of Prince Joffrey. He does about anything the Prince commands him to do, including the murder of a peasant boy that Joffrey disliked. This makes Arya Stark vow to return the favor.
But we learn this his brother, Ser Gregor is a far worse person, and even taller and stronger than Sandor. He also gave Sandor a horrible set of scars from a fireplace during their childhood. Still, Sandor is able to fight almost equally against his big brother. Their first fight is pretty darn good.
But for most of the early part of the series, he remains loyal to Joffrey and House Lannister. Until his fear of fire during the battle against Stannis Baratheon causes him to run scared. But he’s sure to tell Joffrey that he hated him before Sandor leaves King’s Landing.
He manages to bump into Arya Stark and she becomes his hostage for a good number of months. He tries to take her to the Vale, so her aunt will give him gold. But she dies, and there’s no point. Eventually the two start to trust and respect each other, as some of the weirdest “friends” ever.
To the point where Sandor protects Arya from everyone who tries to hurt her in any way. Though he was unwise to mistrust Brienne of Tarth, whom defeated him in battle to the point where he was almost certainly a goner.
But he cheats death and returns to fight. This is mostly against the Night King and the undead. He certainly proves to be very useful (despite some dumb mistakes like throwing rocks to make the wights brave enough to rush at them) and protects some key heroes during moments.
He makes his peace with Arya before he fights his brother in a duel that doomed them both. I didn’t really like Cleganebowl, as fans predicted and called it before it ever happened. It wasn’t very exciting, too brutal, and was rather pointless. The Mountain would have been defeated by Drogon eventually, so this feud was a little dumb to finish. Also a bit of a waste for a character who went from semi-evil to semi-good.