One of the rights reserved for the copyright owner is the ability to make derivative works. This is most obvious in the form of fiction, where fictional characters are cast in events to create a story. As long as a fictional character is sufficiently sketched out, it is a proper object of copyright.

For instance, you couldn't use the Harry Potter characters in your own work without permission. This is one of the rights reserved to the copyright owner. The right to create derivative works also encompasses the creation of other forms of work based on the original, such as movies or TV shows or even merchandise bearing the likeness of the characters. For years after the death of Sir Arthur Conan Doyle, anyone who wanted to use the Sherlock Holmes character had to have permission from the estate. As an author, you too are afforded the protection of your fictional characters. By the same token, you must take care not to violate the copyright of others.