What is the proper noun for author?

There isn't a single proper noun that universally refers to all authors. The closest equivalent would be to use the author's name itself.

For example:

* Jane Austen is a famous author.

* Stephen King is a prolific author.

However, you can use "the author" to refer to a specific author in a context where their name is already known.

Examples:

* "The author's latest book is a bestseller." (Here, "the author" refers to a specific author mentioned previously).

* "The author will be signing copies of their book at the bookstore." (Again, "the author" refers to a specific author mentioned previously).