J.R.R. Tolkien made up orcs. They're human-like in shape, with gray or green skin, angry features, and warlike natures. Now they're used in lots of books and games, including Dungeons and Dragons, the Warcraft series, and even Terry Pratchett's Discworld books (I very much enjoyed Unseen Academicals, which features an orc as the main character). Yay orcs!