Use this hook:

        $user = elgg_get_logged_in_user_entity();

        elgg_unregister_menu_item('topbar', 'profile');
        elgg_register_menu_item('topbar', array(
            'href' => "/profile/$user->username",
            'name' => 'account',
            'text' => $user->name,
            'title' => $user->name,
        ));

Thanks RvR. Will research about "hooks" and try and figure out what script to add it to.

Try my 'dumbest' plugin

In start.php add above code instead of

Line 18: elgg_unregister_menu_item('topbar', 'profile');

if you want to move it left or right in the top bar then add this to the array

'priority' => 10, // this will put the username on the left side of the image

Many thanks RvR - works like a charm! Only thing is the user avatar is gone but that really doesn't matter.

Cim, priority not needed as it's exactly where I wanted it. Good to know for future though - thanks.

@jon666 I've thinked that you want replace avatar with username :)

If you want to display avatar and username both then you need this code:

        $user = elgg_get_logged_in_user_entity();

        elgg_unregister_menu_item('topbar', 'profile');
        elgg_register_menu_item('topbar', array(
            'href' => "/profile/$user->username",
            'name' => 'account',
            'text' => "<img src=\"{$user->getIconURL('topbar')}\" class=\"elgg-icon elgg-inline-block\" alt=\"$user->name\"/>" .$user->name,
            'title' => $user->name,
        ));

just comment out or remove this line of code

        elgg_unregister_menu_item('topbar', 'profile');

@RvR

Trying to do this to display both Avatar and Name for logged in User.. am using Elgg 1.8 with Social Login

Made a plugin and could activate it via Admin login .after activation the Admin User Icon and Name come up fine. But after Admin logs out, there is simply a blank page.. once the plugin is deleted, normal behavior resumes.

How to correct ? pl advise...am a just cut and paste coder so all details much appreciated, thanks!