Most likely one of the three first achievements that you will receive in the game.
When you start a new game, one of the first actions that you will take is to Create/Customize your character. Do so and (I think) after saving the game, you will be rewarded with books for your game play:
- Book of Swords
- Book of Horses
- Book of Bows
Receiving these books will also unlock the three achievements by the same name.