From Halopedia, the Halo wiki

A bureaucrat is an user that can assign or revoke user rights and rename user accounts. They also have the same abilities as an administrator.

How do I become a bureaucrat?

Like administrators, bureaucrats are usually selected on an as-needed basis only, but in the cases that they are selected they are usually given to an administrator if the other bureaucrats agree that adding another one is appropriate.

Alternatively a bureaucrat can also pass on their status to another administrator if they are retiring from being an administrator.

Bureaucrats' help guide

Meet the bureaucrats!

If you need to contact the bureaucrats, you can do so on their talk pages or social boards.