Towards the end of Neverwinter Nights: Hordes of the Underdark
you're trapped in one of the planes of Hell and must seek out a being called the Knower of Names to escape. You can spend huge amounts of gold (anywhere from 100,000 to 500,000 apiece) to learn the true names of many of the NPC's and then have complete control over them. For instance when reach the big bad demon at the end of the game, rather than fighting him you can simply speak his true name and then command him to kill himself. Fun stuff.