Although many studies of personality and aggression focus on multidimensional traits and higher order personality disorders (e.g., psychopathy), lower order, unidimensional traits may provide more precision in identifying specific aspects of personality that relate to aggression. The current study includes a comprehensive measurement of lower order personality traits in relation to three forms of aggression: reactive, proactive, and relational. Traits related to interpersonal antagonism and impulsivity, especially impulsive behavior in the context of negative affect, were consistently related to aggression across multiple indices. These findings suggest that certain lower order traits are of critical importance to understanding who engages in aggressive behavior and why this behavior occurs. (Contains 3 tables and 1 note.)