What do you call a person who writes book on your behalf?

There are a few terms you could use to describe someone who writes a book on your behalf, depending on the specific context:

Formal:

* Ghostwriter: This is the most common and widely understood term. It refers to a writer who writes a book under someone else's name.

* Collaborating writer: This term implies a more collaborative process, where you might have more input and ownership of the content.

Informal:

* Book doctor: This term is sometimes used for writers who help polish and revise a manuscript, but can also refer to someone who helps with the overall structure and content of a book.

* Scripter: This is a more casual term that emphasizes the act of writing, but doesn't necessarily imply anonymity.

Ultimately, the best term depends on the specific circumstances and the level of involvement of the person writing the book.