It isn't that he is 'considered' famous; more that he actually IS extremely famous. Whichever country in the world you visit, Shakespeare's name will be known. Similarly, if people can only name one playwright, it will be Shakespeare. His work features on the curriculum of schools and colleges the world over.
His plays have been performed year in, year out by amateurs and professionals worldwide, as well as in the theatre dedicated to him. There are writers, actors and academics whose work is specialised solely upon Shakespeare/ That is surely the ultimate in fame?