A baby arrives in America from a home in turmoil. A family in Kansas raises him. And he struggles to balance two identities. Comic books, TV shows and films have repeatedly recounted these details from Superman’s backstory over the past 87 years. But the director of the latest big-screen adaptation drew backlash recently when he stated something that’s been said many times before: Superman is an immigrant. “I mean, Superman is the story of America,” director James Gunn told The Times of London. “An immigrant that came from other places and populated the country, but for me it is mostly...