Gravity Forms - Populate Name Field - Using Dynamic Population Parameters

functions.php

add_filter('gform_field_value_first_name', 'eo_populate_name');
add_filter('gform_field_value_last_name',  'eo_populate_name');

function eo_populate_name($value)
{
  // extract the parameter name from the current filter name
  $param = str_replace('gform_field_value_', '', current_filter());
  
  // we are interested only in the first_name and last_name parameters
  if ( !in_array($param, array('first_name', 'last_name')) )
    return $value;

  // incidentally, the user meta keys for the first and last name are
  // 'first_name' and 'last_name', the same as the parameter names 
  $value = eo_get_usermeta($param);
  
  return $value;
}