Create a user account in Drupal 7 programmatically

gistfile1.php

<?php
//This will generate a random password, you could set your own here
$password = user_password(8);

//set up the user fields
$fields = array(
  'name' => 'user_name',
  'mail' => '[email protected]',
  'pass' => $password,
  'status' => 1,
  'init' => 'email address',
  'roles' => array(
    DRUPAL_AUTHENTICATED_RID => 'authenticated user',
  ),
);

$fields['field_first_name'][LANGUAGE_NONE][0]['value'] = 'First Name';
$fields['field_last_name'][LANGUAGE_NONE][0]['value'] = 'Last Name';

//the first parameter is left blank so a new user is created
$account = user_save('', $fields);

// If you want to send the welcome email, use the following code

// Manually set the password so it appears in the e-mail.
$account->password = $fields['pass'];

// Send the e-mail through the user module.
drupal_mail('user', 'register_no_approval_required', $email, NULL, array('account' => $account), variable_get('site_mail', '[email protected]'));

// (c) http://codekarate.com/blog/create-user-account-drupal-7-programmatically