"The Age of Heroes" is a featurette and part of "History & Lore" section of the Complete Guide to Westeros, a special feature in the blu-ray of Season 1 of Game of Thrones. It is narrated by Isaac Hempstead-Wright as Bran Stark.
When Aegon the Conqueror launched his invasion of Westeros he faced seven independent kingdoms: the Kingdom of the North, the Kingdom of the Mountain and the Vale, the Kingdom of the Iron Islands and the Riverlands, the Kingdom of the Rock, the Kingdom of the Reach, the Kingdom of the Stormlands, and Dorne. Some of these kingdoms had been established thousands of years before, in the Age of Heroes.
Other legends speak of the Grey King in the Iron Islands, who took a mermaid to wife and defeated Nagga, the first sea dragon. House Greyjoy of Pyke, current rulers of the Isles boast descent from him.
The Reach and all its fertile lands were first ruled by House Gardener. Garth Greenhand, founder of the House, wore a crown of flowers and vine. He ruled as the first King of the Reach from his seat of Highgarden and was said to have made the land bloom. Many noble houses trace their descent back to him, including House Tyrell, the current lords of Highgarden.
Certain ballads of the Stormlands tell of a warrior named Durran who fell in love with Elenei, daughter of the God of the Sea and the Goddess of the Wind. She became a mortal after giving him her maidenhead. Enraged, Elenei's parents called upon a massive storm and destroyed Durran's bayside keep as a "wedding gift". Durran declared war on the gods and rebuilt his keep, which was also destroyed. He raised four more castles, each stronger than the previous but all these too fell to the power of the gods. Durran's seventh castle, however, withstood the gods' rage. Durran became known as "Durran Godsgrief" and reigned as the first Storm King.
There are countless other tales from the Age of Heroes, histories never recorded in a book but passed from generation to generation through stories and songs. While some of them may be dismissed as fairy tales, each of the Seven Kingdoms is nevertheless defined by them.