Thief is a venerable series started by the well respected and now sadly demised Looking Glass Studios. The first game, Thief: The Dark Project, not only introduced us to the world where magic and steam-punk technology uneasily co-exist but it also ushered in the concept of stealth based gameplay. It was the first first-person shooter that actively de-emphasised the shooter aspect to become its own genre - the first-person sneaker. Here the goal wasn't to kill your enemies, but rather bypass them by distracting or knocking out them out and hiding the unconscious body where other guards wouldn't find it. This was quite a revolution and directly lead to the rise of stealth-oriented segments in other FPS games.