If you look a drupal node, drupal displays the author of this node as the username of the user or anonymous if the author is not registered user. Now if we want to display the real name of the user (a field we will add in the profile module) instead of the username, drupal provides a theming function that let's you modify the output of the username before it is printed on a node. Let's see how we can do this.

I'll go directly to the code

This one goes in your template.php (under sites/all/themes/yourtheme/).

function phptemplate_menu_item_link($link) {
  if (empty($link['localized_options'])) {
    $link['localized_options'] = array();
  }
  if (empty($link['localized_options']['attributes']['class'])) {
    $link['localized_options']['attributes']['class'] = 'menu-'. $link['mlid'];
  }
  else {
    $link['localized_options']['attributes']['class'] .= ' menu-'. $link['mlid'];
  }
  return l($link['title'], $link['href'], $link['localized_options']);
}