Welcome to Aloriand! You've been summoned by a Demonlord to fight for his great cause of complete world domination, and in exchange, he will give the life you've always wanted.
The Pact states that you play as his Champion and do his bidding. Of course, this comes with a few perks — curses blessings that the Demonlord has given you himself, powerful skills that would help you carry out his will, chance to pillage villages, murder heroes and access to tons and tons of richess.
The journey wont be easy. You will find yourself constantly buggerred by Heroes whose main goal is to stop you at all cause. Not only that, you need to tend to the Demonlord's growing village, the only people who believe in your cause. You will need to defend them, command them, and help them get on through whatever problems they encounter in life. This could sound a lot like having a child at first, but trust me, it gets better.
Right, I see you haven't ran away screaming in fear yet. Very well, let's get this evil adventure going then.