Thousands of years ago, Lew Therin Telamon fought the Dark One. In the end, he won the struggle, but the cost was great. Saidin was tainted. In the world of the Wheel of Time, there is a magic divided into two halves, Saidin and Saidar. Certain people at random (genetically?) can access one half or the other of the "True Source". Males use Saidin, and females use Saidar. When the Dark One tainted Saidin, he made it such that any male who channels it goes insane eventually.
Awesome, isn't it? Now, take a world with something like thousands of magic users. Now, strip half of them of their sanity, but leave them with their magical powers. Yeah. This lead to the Breaking of the World, which reshaped mountains, moved oceans, and destroyed most of civilization. In the years since, humans have built themselves back up, but it's been a long and difficult process, slowed by many wars.
Lews Therin Telamon went insane before he died too, and killed all of his family, earning him the name Lews Therin Kinslayer. He is also named The Dragon. There is a prophecy that says The Dragon will be reborn again. And when he does, the Dark One will break free once again, and they will fight. In his attempts to defeat the Dark One, The Dragon Reborn will break the world once again. And his victory is not certain.
"The Wheel of Time turns, and Ages come and go. What was, what will be, what is, may yet fall under the Shadow. Let the Dragon ride again on the winds of time."
The Dragon has been Reborn. The time has come. The Wheel of Time by Robert Jordan and Brandon Sanderson tells this tale. I highly recommend it. I guess after giving the background today, I'll be giving my impressions tomorrow.