The phrase "anonymous author" refers to someone who writes a book, article, or any piece of writing, but their identity is not known or revealed. They choose to remain unknown to the readers. Full definition
The 13th - century anonymous author of Mirror for Simple Souls writes,» This night is nothing less than the Trinity itself, showing its inner being to the soul. (religion-online.org)
All we know about Jesus comes from 4 short stories written 50 - 130 years after his supposed crucifixion by anonymous authors who couldn't have known him personally, who radically disagreed with each other about what happened during his life. (religion.blogs.cnn.com)
Initially Reena Spaulings was the title of a novel written by an undisclosed number of anonymous authors from the circle of the artist collective Bernadette Corporation. (artnews.com)