Grégory Viguier

<p>With this plugin, administrators can change the default author base in the registered users profile url, and the author slug of each user.<br />
Changing an author slug is a good thing for security (if your login is “This Is Me”, your slug will be “this-is-me”, a bit easy to guess).<br />
The plugin adds 2 fields for this purpose, one in permalinks settings, the other in a user profile.</p>
<ul>
<li>Default: <em>example.com/author_base/author_nicename/</em></li>
<li>Customized: <em>example.com/jedi/obiwan/</em></li>
</ul>
<h4>How to edit the slugs</h4>
<ul>
<li>Go to <em>Settings</em> > <em>Permalinks</em> to edit the author base: “author” => “jedi”</li>
<li>Go to <em>Users</em> > <em>“Any user profile”</em> to edit the user slug: “agent-smith” => “obiwan”</li>
</ul>
<h4>Translations</h4>
<ul>
<li>English</li>
<li>French</li>
<li>German by <a href="https://wordpress.org/support/profile/carny88" rel="ugc">Carny88</a></li>
<li>Spanish by <a href="https://wordpress.org/support/profile/oliverbar" rel="ugc">Oliver</a></li>
</ul>
<h4>Multisite</h4>
<ul>
<li>The plugin is ready for Multisite.</li>
</ul>


SF Author Url Control

Allows administrators or capable users to change the users profile url.

Konstantin Obenland

<p>This plugin replaces the author slug with a sanitized version of the user’s display name.</p>
<p>This plugin will not prevent hackers from finding out your login name but the login name won’t be visible<br />
in the author archive’s URL, which works towards your friendly URLs with using your display name.</p>
<p>DO NOT use this on a site with more than 1000 registered users, as updating all of their nicenames at once might break your site.</p>


WP Author Slug

Easy way to add some obscurity to login guessing.

But please update as it's over 2 years now.

Excellent

This plugin would probably work OK if you have a small number of users (e.g. if your site doesn't allow public login). But if you have a large number of users (e.g. if you are running ecommerce or allow users to register for other reasons), this plugin will probably take down your site.

The reason is that there are hooks that run when you activate or delete the plugin. It runs database fetch and update queries on every user in your database, all in-line on the request (rather than background via a cron). So if you have a thousand or more users it attempts to do a thousand or more database writes when you click Activate or Delete from the plugins list. This will likely grind your website to a halt. 

It would be better/useable if you could either choose to only apply these scripts to specific user types (e.g. Author) or if you could run the update in batches in the background.

Don't use if you have a large user database

Add a layer of security and prevent your login name from being shown in the author archive's URL.

SF Author Url Control vs WP Author Slug