For a Wordpress organization website, I want all the posts to have by default the same author name (the organization name). How can I achieve this behavior?
There are multiple possibilites.
1) Simplest: You only create one author and share the login within the organization
2) You simply do not display the author on your post - why would you do that? It is probably obvious that your organization is the publisher of these pages anyway.
3) Add the following custom code within your Theme or Plugin:
add_filter('the_author','its_my_company');
function its_my_company() {
return 'Organization Name';
}