All of my rivals have been named S. When I first began Red, I didn't want to use the typical rival names that my friends used (like "Douche"), nor did I want to go with one of the preset names. I decided to pick a letter of the alphabet that I disliked, and for some reason, I settled on S. I'm not sure why I disliked the letter S (it's not my favorite letter, but it's probably in the top 50% at this point, or at least not in the bottom 25%), but it stuck. I have used it in every game since then, and when I started up Red a couple of days ago, I entered it without really thinking too much of it.