In case someone famous created an altcoin, but not someone famous like Linus Torvald or whatever obscure cryptographist, no someone that is mainstream, like Rihanna, would it be a threat to Bitcoin ? You could be sure that masses of people would come to use Rihanna's payment system, as it would be branded. Or at the inverse would that be the door for millions of people to know what Bitcoin is and make them understand that this is a great progress ?