Well, it depends on how specific your fairies are. A couple Tuatha de Danann (who probably were the foundation for the kings were Bres, Lugh, and Nuada. The king of the Tylwyth Teg was Gwyn ap Nudd. Either he or Arawn (another king) led the Wild Hunt. And if you just don't want to use the name Oberon, you can always go with Alberin or Alberich.