The invisible stalker are ethereal beings that make their home in the Twisting Nether. They can be summoned by druids as nature's allies.
In World of Warcraft
Strangely enough invisible stalkers are apparently in World of Warcraft. They are as their name suggests, completely invisible and undetectable. They are completely harmless level 1 mobs. They are apparently located in several places and act as invisible triggers that activate certain things in game.