Few creators have left as profound a mark on popular culture. According to The-Numbers, a box office data site, films featuring Mr. Lee’s superheroes have grossed more than $24 billion worldwide. “Stan is right up there with Walt Disney as one of the great creators of not just one character, but a whole galaxy of characters that have become part of our lives. Right now, I think he’s probably bigger than Disney.” Yet at the summit of Mr. Lee’s career, storm clouds have gathered.