I thought this short analysis helpful.
I can appreciate this final paragraph.
According to Aristotle, states may be classified according to the number of their rulers and the interests in which they govern. Rule by one person in the interest of all is monarchy; rule by one person in his own interest is tyranny. Rule by a minority in the interest of all is aristocracy; rule by a minority in the interest of itself is oligarchy. Rule by a majority in the interest of all is “polity”; rule by a majority in its own interest—i.e., mob rule—is “democracy.” In theory, the best form of government is monarchy, and the next best is aristocracy. However, because monarchy and aristocracy frequently devolve into tyranny and oligarchy, respectively, in practice the best form is polity.
Plato’s Republic would be a wicked, tyrannical oligarchy.