Protect Admin User

	class Protected_User {

    // Select capabilities from the default 'Administrator' role

    public function __construct() {

        add_filter('editable_roles', array($this, 'filter_editable_roles'));

        add_filter('map_meta_cap', array($this, 'filter_map_meta_cap'), 10, 4);

    }

    // Remove 'Administrator' role if the current user is not a protected user

    public function filter_editable_roles($roles) {

        if (isset($roles['administrator']) && !current_user_can('administrator')) {

            unset($roles['administrator']);

        }

        return $roles;

    }

    // Prevent edit, delete or promote from 'Administrator' capabilities 

    public function filter_map_meta_cap($caps, $cap, $user_id, $args) {

        // Define the ID of the protected 'Administrator' user (Example 1)

        $protected_user_id = 1; 

        switch ($cap) {

            case 'edit_user':

            case 'remove_user':

            case 'promote_user':

                if (isset($args[0]) && $args[0] == $protected_user_id) {

                    if (!current_user_can('administrator') || $user_id !== $protected_user_id) {

                        $caps[] = 'do_not_allow';

                    }

                }

                break;

            case 'delete_user':

            case 'delete_users':

                if (isset($args[0]) && $args[0] == $protected_user_id) {

                    if (!current_user_can('administrator') || $user_id !== $protected_user_id) {

                        $caps[] = 'do_not_allow';

                    }

                }

                break;

        }

        return $caps;

    }

}

new Protected_User();