The Great Houses are the most powerful of the noble houses of the Seven Kingdoms. They exercise immense authority and power over their vassals and territories and are answerable only to the King of the Andals and the First Men, Lord of the Seven Kingdoms and Protector of the Realm.
House Baratheon of Storm's End is a legally extinct Great House of Westeros. Its main branch was formerly the royal house, but House Lannister now controls the throne. House Baratheon's sigil is a black stag on a gold background and their house motto is "Ours is the Fury". When Robert ascended to the Iron Throne, a gold crown was added to the stag, denoting their status as the royal house.
House Stark of Winterfell is a Great House of Westeros, ruling over the vast region known as the North and the Vale as Kings in the North from their seat in Winterfell. It is by far one of the oldest lines of Westerosi nobility, claiming a line of descent stretching back over eight thousand years. House Stark's sigil is a grey direwolf on a white background, over a green escutcheon. They are one of the few noble Houses whose family motto is not a boast or threat. Instead, the House Stark family motto is a warning, one that no matter the circumstances will always be relevant: "Winter is Coming".
House Lannister of Casterly Rock is one of the Great Houses of Westeros, one of its richest and most powerful families and oldest dynasties. It is also the current royal house of the Seven Kingdoms following the extinction of House Baratheon of King's Landing. House Lannister's Heraldry consists of a golden lion on a crimson background, and their House words are "Hear me roar!", which is rarely mentioned. Their unofficial motto, which is as well known as the official one, is "A Lannister always pays his debts".
House Targaryen is a former Great House of Westeros and was the ruling royal House of the Seven Kingdoms for three centuries, before it was deposed during Robert's Rebellion and House Baratheon replaced it as the new royal House. The few surviving Targaryens fled into exile. Currently based in Essos, House Targaryen seeks to retake the Seven Kingdoms from House Lannister. House Targaryen's sigil is a three-headed red dragon on a black background, and their words are "Fire and Blood".