Here is the Unique in question (the name and suffix are randomly generated). They have better stats and are better at fighting than normal creatures of their type:
When you kill an Unique, the other creatures on the level won't forget it:
I don't think I will make hard-coded Uniques (like Sigmund). Eventually, Uniques will have a chance of carrying magical items, and will affect Monster AI for those creatures in LOS to them. Perhaps they might even drop unique items (for example, "Preald's Goblin Totem"?).