And when you play using this setup in the Golarion System setting, I'm sure none of the DSP staff would hold it against you if you decided that that was the great evil in question. However, given that this is not a book for that setting, that Rovagug is a very setting specific kind of evil (even ignoring the fact that as a copyrighted name DSP actively couldn't use Rovagug even if they wanted to), and it is in fact ultimately a setting agnostic book designed for use in anything from Golarion to old Starjammer stuff to the crazy stuff I concocted at 3 AM in my basement the other night, it is far more sensible to leave it as a vague, mysterious, nebulously defined evil and leave it at that.