Wikipedia:NOSHARE

You choose your username when creating a user account. All contributions made using that account will then be attributed to the chosen username (contributions made while not logged in to any account are attributed to the user's IP address). It is also possible to request a change of username, and have your past contributions re-attributed to the new name.

The following types of usernames are prohibited:

Bear in mind that, once chosen, a username cannot be easily changed. If you choose "Dr. Franz Schröder", then your doctorate will be evident on history pages and, unless you change your signature, on all posts to talk pages. If you prefer to be less formal, leave off the title. However, you should read the section on using your real name as your username.

The software will not allow you to register with a username that is already in use, or one that appears too similar to one that is already in use. In the latter case, however, you may still request permission to use that name (see § Similar usernames below).

Your username can be virtually any string of characters (subject to a few technical limitations). However, it should be a name which other users will be comfortable with and which does not interfere with the project. A controversial name may give a bad impression to other users, and avoiding this is in your own interest. This page describes certain types of usernames that are specifically disallowed, primarily because they can be considered offensive, misleading, or promotional, or imply that the account does not belong to an individual.

This section lists the types of usernames that are considered inappropriate. The same criteria also apply to signatures.

These lists are not necessarily exhaustive. Use common sense in applying these rules (such as a word that may seem offensive in one context may have another, more benign meaning in another context). For guidance on how to deal with inappropriate names if encountered, see § Dealing with inappropriate usernames below.

...
Wikipedia