Current Page Author ID

Hello,

How can I get the shortcode to display information for the current page author ID?

For example:

[user_firstname id=2] will display the first name of user #2 (User) when he is on the “Books” page let’s say. But what if I wanted to do something like [user_firstname author_id=2] to display the name of the page author of the “Books” page (Author) no matter which user is visiting that page?

Thanks in advance for your help!