"At" is not the stem you're looking for- it's -krat/crat, which means "rule" in Greek. An autocrat is a "self-ruler", i.e. they rule by themselves, so it's roughly synonymous with monarchy ("rule by one"). I don't really understand what you're asking, anyway- these "titles" aren't really tiered as such, and you have to keep individual context in mind- a Byzantine Autokrator is different from Soviet autocracy, for example.