Gregor Clegane (Game of Thrones)

Gergor is one of the most fearsome warriors in Westeros, partly because, at over seven feet, he towers over other men. He is Tywin Lannister's chief enforcer, and is often referred to as "The Mountain that Rides" or simply "The Mountain".

Background
Gregor is an extremely violent and cruel man, and is prone to fits of rage. When he was only eleven years old he burned his little brother Sandor by forcing his face down into burning coal as punishment for taking a discarded toy knight. At this age he was already six feet tall, and it took several grown men to tear him away from his little brother. It probably goes without saying that there is no love between the two brothers. It is also rumoured that he was the one to rape and murder the former king Aerys Targaryen's wife, along with their children.

Major Plots
In the tourney to celebrate Eddard Stark's appointment as Hand of the King, Gregor kills Ser Hugh of the Vale, but is unhorsed in the final joust by Loras Tyrell. Enraged by his loss, he beheads his horse with a single strike and attacks Loras. Sandor steps in to stop his brother, and the two have a short sword fight that is cut short by King Robert. Some time later, common folk from the Riverlands come before Ned Stark and plead for help to stop a band of raiders. Based on their description, Ned believes Gregor to be their leader and sends Beric Dondarrion to stop him.