There are many great programmers in the world. I don’t think it’s fair to attribute a single person for being “the greatest”. Programming is such a massively broad topic that covers a wide spectrum of categories - operating systems, graphics, web development, embedded systems, and many more. And with each category comes exceptionally talented individuals who stand above the others. If you want to find a small sample of these individuals, just take a look at those who were inducted as ACM Fellows. Each of the individuals who are part of this have made outstanding contributions to a particular field, or many fields. They are all considered “the greatest”.