Napoleon in "Animal Farm," e.g (6)
(Other definitions for pig that I've seen before include "Hog" , "Farm animal" , "Mass of metal simply cast" , "Greedy eater" , "Domestic swine" .)
(Other definitions for tyrant that I've seen before include "Autocrat - bully" , "Autocrat or despot" , "bully - with 17d" , "big bully" , "Despot, dictator" .)