Since there are countless scary stories out there that could potentially be considered the 'world's most scary story', the author could be anyone. It could be a contemporary writer who has a knack for creating truly terrifying scenarios, or it could be from a long - forgotten era, written by someone whose name has been lost to time. There are also many different cultures with their own horror traditions, so the author could be from any of those cultures as well.
There could be many stories that claim to be the 'world's most scary story', so it's difficult to say who the author is. It might be a well - known horror writer like Stephen King if it's a popular modern horror story. But if it's an old, traditional scary story, it could be from an anonymous source passed down through generations in a particular culture.
I'm not sure which specific 'world's most scary story' you are referring to. There are many scary stories in the world, so without more context, it's hard to determine the author.