A games development studio based out of Cambridge, Massachusetts. They recently (May 24, 2000) closed their doors for good, to the dismay of many of their long time fans.

Looking Glass was the creator of many great PC games.

-Ultima Underworld
-Ultima Underworld 2
-System Shock
-Flight Unlimited
-Terra Nova
-British Open Championship Golf
-Flight Unlimited 2
-Flight Unlimited 3
-Thief
-System Shock 2
-Thief 2

I believe they also worked on a Road & Track racing game in the early 90's (not Need For Speed).

The games listed above were, for me and a lot of other people, some of the greatest games ever made. Ultima Underworld was out around the time of Wolfenstein, but you could jump in UU. System Shock was out around the time of Doom, and along with being an ammazingly massively immersive RPG, it also included sloped surfaces, something which Doom did not.