You need to finish G/F end if you haven't already, several people talk about crawling one in those endings. As for creators and rulers, I think that is mainly mentioned in dlc 2 content which is mabel and her dungeon, specifically the info dump after you beat old king and the books in the library level of the dungeon. Also a little bit about creators in G/F ends from Jabberwock if you trigger that fight.
Speaking of the G/F end jabberwock fight, if there is one thing I really like about this game, it's the dialogue and presentation of some boss fights. Abominabal Jabberwock (Let's face it, if inferior humans can do it...), Chaos dungeon Hellkaiser (that intro and transition to phase 4), Vorpal (intro, boss sprite, the music), Mary sue in BS 1(There's no next page even if you kill me, only the back cover.) are all great in that regard.
Beat Kuti or get it from chaos dungeon.