Charles K. Mills is a notable author whose pen name is not detailed in the provided Wikipedia extract.
The provided Wikipedia text focuses on the concept of pen names, also known as pseudonyms or nom de plumes, and their various uses by authors. It explains that authors may adopt these alternative names for reasons such as enhancing distinctiveness, concealing gender, separating different bodies of work, avoiding repercussions for their writing, or consolidating multiple authors under one name. The text also mentions that the true identity of an author using a pen name might be known only to their publisher or could become publicly recognized over time. However, the extract does not offer specific details about Charles K. Mills himself, his works, or any particular pen names he may have used.