We can display user's identity based on their properties other than username, including actual name, email address, or user ID using the module RealName .
Steps for configuring RealName for drupal 7
For using RealName we have to activate the Token module first, since the module completely relies on the Token API.
In the configuration page of the RealName module add whatever token you need to display instead of username in the 'Realname pattern' text field. You will get all available tokens by clicking the link 'Browse available tokens.'
You can test this change by trying to post comment for an article. The specified token value would be shown instead of default username.
You may also look into other solved issues related to Drupal module configurations over here.