d4d24a6c__update_user___WordPress_Codex_n_contain_the_following_fields_Description
[Field Name] display_name [Associated Filter] pre_user_display_name [Description] 
A string that will be shown on the site. Defaults to user's username. It is likely that you will want to change this, for both appearance and security through obscurity (that is if you dont use and delete the default admin user).
Function Reference/wp update user « WordPress Codex
Description