Yep, nobody knows that better than the Star Trek & Star Wars moguls. They tried slapping fan producers down until they realized that was bad for business, so now it's pretty much live & let live -- as long as nobody but Lucasfilms & Paramount makes any money from Luke Skywalker & Captain Kirk. Which is fair enough since it's their property. Regarding Snape & Potter, well there's no law against creating & distributing a generic Alchemist & Apprentice type character. Those are folklore concepts and therefore in the public domain. Even if it can be made to somewhat resemble JKR's or Warner's versions. Heck, if being a look-alike, celebrity or not, is a copyright violation, shouldn't folks who are twins be arrested?