Personality is one of the six raw abilities that determine how your Hero can interact with the world.
Personality determines how persuasive your character is when talking with other characters, as well as his or her likeability and leadership ability. One's Personality score has a direct effect on the outcome of certain dialog choices, and may make new dialog options available if high enough. It also directly affects the number of teammates your Hero can command in battle at any one time. A Personality of 15 is required to have 8 teammates, the maximum possible. Plus, the starting Gold of Hero in the game depends on his Personality.