Alright, so 'Buku Il Principe' - that threw me for a second because I think the asker might mean 'Il Principe' by Machiavelli, but 'buku' is Malay/Indonesian for 'book'. If we're talking about that classic political treatise, 'key characters' is a bit of a funny way to put it since it's non-fiction, but the book itself personifies concepts.
Machiavelli spends a lot of time talking about Cesare Borgia as his prime example of a 'new prince' who used force and cunning to secure power, only to have it all undone by bad luck and illness. He's the most fleshed-out 'character' in the whole thing, almost like a tragic hero in Machiavelli's analysis.
Then there's the contrasting figure of Agathocles of Syracuse, who's held up as someone who achieved power through wickedness and cruelty. Machiavelli uses him to make that infamous point about whether it's better to be loved or feared. So those two historical figures really carry the argument forward, more than just abstract ideas.