Really better than making static personality types, I think it better to have personality attributes with a range of values. Then certain canon personalities can be crafted within that system, but also other personalities and random personalities.
Examples:
Honor: high rating means they keep their word, low means not so much.
Expansionist: high score wants to grow borders, low score turtles.
Risk taker: Will the AI go balls to the wall, or play it safe?
Share the essence: keeps essence with channeler or makes lots of weaker heroes.
Lawful vs chaotic for all you D&D fans
Vindictive vs forgiving (yes being forgiving could actually be advantageous, maybe diplo bonus for forgiving and forgetting)
Also most of the racial attributes for GalCiv2 and others could come into play.