Why is the orc the iconic face of Dungeons and Dragons humanoids? In large part it has to do with Tolkien's treatment of them in the Lord of the Rings and Hobbit, but not all the responsibility can be laid at the feet of those two works. It goes beyond just official orcs also. Anyone can create something, but for it to catch on it has to resonate somehow with humanity. A hallmark of fantasy is a large violent humanoid race that exists in the wilds, uncivilized, in competition with man. Why?
I had a realization the other day about this very question. Human beings have evolved several traits to procure food in a very successful manner. Large brain mass so that we could remember where all the good fruit is. Various adaptations that make us good at tool use and adaptation in differing climates.
At some point in the past there was a break, a differing path of evolution of man. One branch developed teamwork, squad level tactics, along with excellent communication skills. They perfected weapons like spears, and traps like deadfalls. They had thick dense bones, and generation and generation they developed more and more powerful musculature. They perfected techniques that allowed them to bring down the largest and most violent animals. They were strong and quick and smart.
The other developmental path taken was wiry, thin, and good at running. Relaxed, with no skill at weaponry or combat. Constantly on the move. We must have seemed strange to our neanderthal cousins who were superior to us in almost every way. Then something happened.
It got warm. As the large game animals retreated into the forests, the neanderthals began to starve. You couldn't back an antelope into a canyon trap, they was a herd and they were too fast. Meanwhile, our adaptations (heat dispersion though the skin, the arch of the human foot, our endurance) allowed us to run our food to death, practically at will. Their food source literally disappeared. Soon enough, so did they.
But they didn't disappear from our memory. Beings, like us, strong, bestial, and warlike. Brutish, physically superior to us in nearly every way. Gone, but not forgotten.
Is it any wonder why it's such a powerful image?