ˈghost ˌwriter noun [countable] someone who is paid to write a book or story for another person, who then says it is their own work
—ghost-write verb [transitive] [TahlilGaran] Dictionary of Contemporary English ▲
ghost writer n. A writer whose identity remains a secret and who writes for another who receives all the credit.
It is rumored that John Smith's best-selling novel was written by a ghost-writer. [TahlilGaran] English Idioms Dictionary ▲