Skidvar’s Random Personalities
"Skidvar’s RAP – Random Personalities" gives rival factions random (faction) personalities depending on the faction leader at campaign start and whenever a faction leader dies, cf. Attila. (The only exceptions to random personalities are the immortal generals (with the "great leader" trait)
In other words, the aggressiveness and reliability of your surrounding factions will be different in the beginning of every game, which adds a lot to replayability. But these factors may change during the game when a leader dies, so now you may want to keep certain reliable allied leaders alive, while having certain powerful aggressive enemy leaders killed.
Required items: Skidvar’s Vanilla Scripts. More info there.