What we once called a German Shepherd is now, with annoying precision, officially called a German Shepherd Dog. This is, evidently, intended to distinguish the breed from the more common German Shepherd Fish and German Shepherd Telephone.
German Shepherds are descended from a long line of sheep-herding dogs of various abilities and appearances, but the breed was standardized beginning in 1899 by an obsessive character named Max von Stephanitz, who inbred them to the point that several of the offspring actually collapsed and spontaneously combusted. Max nevertheless persisted, and the German Shepherd is today the third-most popular dog in the United States, ranking just below Yorkshire Terriers and just above Golden Retrievers.
Modern German Shepherds seldom herd sheep, who are now heavily unionized and have ironclad contracts with wolves that limit predation to a specified level. Each flock now has a Sheep Steward whose function is to make sure the sheep uphold their end of the contract, and to convey grievances to management. So German Shepherds have long been associated with other parts of the security industry; when I was growing up, if you said "Police Dog" this is the breed you were talking about.
Rescue: German Shepherd Rescue