Find the user who initially created the post

There are several approaches to your issue.

1- Getting the original author inside a loop

To retrieve the original author of a post inside a loop, you can use get_the_author(); to get the username of the author or $post->post_author(); to get his/her user id. If you wish to get the revisor’s username or id, you can use the_modified_author(); or get_the_modified_author();.

2- In the back-end

If you want to have this result in the back-end (view the original author in the admin panel), you can use the following plugin made specifically for this purpose.

Published By plugin made by Scott reilly