The raw materials of literary and fictional creation are the real world, the author's experience, the English language and all previous literature and fiction. The creative process begins with an idea and a blank sheet of paper or a computer screen. Its end product is an artifact on sale to the public. Thus, we become familiar with many fictional characters and their settings. Once, they did not exist. There was a time before there was a Sherlock Holmes. I mention Holmes because of his importance to Poul Anderson but we can easily think of many other examples. Stieg Larsson's Girl With The Dragon Tattoo is a much more recent creation.
There are many blank sheets of paper and potential ideas that have not yet been formulated. Creation continues.