The X Window System by default uses the XDM display manager. However, resolving XDM configuration issues typically involves editing a configuration file. GDM allows users to customize or troubleshoot settings without having to resort to a command line. Users can pick their session type on a per-login basis. GDM also features easy customization with themes.
Some of the copyright notices of GDM refer to the "Queen of England", who is also named as a maintainer in release announcements since version 2.2.1. It was only later that the developers realised that there has been no "Queen of England" since the Acts of Union of 1707.
GDM has a few easter eggs, in the form of strings to be entered in the username box. These can be found in the source file "gui/guilogin.c", in a function named "evil".