We Are Many (3.5e Trait)
From D&D Wiki
We Are Many
A man with a broken mind may be unstable, but he will not be controlled
Benefit: Character becomes immune to Mind-Affecting effects
Drawback: At character creation, take an ability score of 5 on either Wisdom or Intelligence. (If rolling your stats and you haven't rolled a 5, convert your lowest roll that is greater than 5, and change it to 5. If using point buy, treat this is a +0 points choice, you do not gain nor lose points for taking a 5.)
Roleplaying Ideas: The character can either be introverted and hide their mutiple personalities or openly express their multiple minds, either path can have adverse affects on relationships within a group.