Ghostwriter

A ghostwriter is the actual author of the book while the cover claims it was written by someone else. The practice of ghostwriting is often applied in autobiographies. The person who's interesting enough to have an autobiography published often does not have the literary skill to make their story into a story that is pleasant to read. Ghostwriting is not the same as plagiarism, which is copying someone else's story without giving them credit, or using a penname, which is writing your own story under an assumed name. A ghostwriter writes someone else's story under their name.

Ghostwriters are (generally) not actual ghosts; they are called that because -- like most ghosts -- they stay invisible. There is no knowledge whether there are any ghostwritten fanfic stories.