who exactly is the roaring knight in deltarune?

Not confirmed yet, Toby has kept it vague on purpose. Most of the fandom thinks it's connected to Kris in some way, since the Knight is the one making new Dark Fountains and Kris is the only other character we've watched open one. The other big camp says it's someone from town we've already met. Chapters 3 and 4 add hints but nothing that settles it, so treat any "it's definitely X" video as a theory.