What is Dwarf Fortress
Dwarf Fortress is known for it's major Simulation aspects. there is a massive amount of things to do as every time you create a new world it generates everything from someone's hobby and family line to towns and countries waging ware. the game comes with 2 modes (there is one more but it is more of a reading section) Fortress Mode where you create a Fortress and help it prosper. and then there is Adventure Mode which is where you create a character and directly affect the world around the Player.
This is an example of a Small World. you can choose from a variety of sizes which can strongly effect the loading time and History Generation Time. You can choose how many races are in and how common towns and other fortresses are. The Map and History Generation is a massive feat for a single man to do. for more information on the World Generation and other things visit the Dwarf Fortress Wiki
As many people have said Dwarf Fortress is one of the most complex games there has ever been. the massive amount of generated items can severely slow down even the best PC.
Who Made Dwarf Fortress?
Dwarf Fortress was make and designed by Tarn and Zach Adams, they have been working on Dwarf Fortress since 2002 on and off but constantly since 2006. Tarn has even claimed Dwarf Fortress 'My Life's Work' Although they work on many other unreleased Projects, Dwarf Fortress is by far their most popular game.
Here are some Links about Dwarf Fortress and it's Creators
Bay 12 Games