The Revv Toparchy, mentioned in the Words of Radiance: Epigraphs for Words of Radiance: Chapter 43, was likely comprised of rulers of some kind.

And thus were the disturbances in the Revv toparchy quieted, when, upon their ceasing to prosecute their civil dissensions, Nalan'Elin be took himself to finally accept the Skybreakers who had named him their master, when initially he had spurned their advances and, in his own interests, refused to countenance that which he deemed a pursuit of vanity and annoyance; this was the last of the Heralds to admit to such patronage.

–From Words of Radiance, chapter 5, page17[1]