When and why do power holders seek to harm other people? The present research examined the idea that aggression among the powerful is often the result of a threatened ego. Four studies demonstrated that individuals with power become aggressive when they feel incompetent in the domain of power. Regardless of whether power was measured in the workplace (Studies 1 and 4), manipulated via role recall (Study 2), or assigned in the laboratory (Study 3), it was associated with heightened aggression when paired with a lack of self-perceived competence. As hypothesized, this aggression appeared to be driven by ego threat: Aggressiveness was eliminated among participants whose sense of self-worth was boosted (Studies 3 and 4). Taken together, these findings suggest that (a) power paired with self-perceived incompetence leads to aggression, and (b) this aggressive response is driven by feelings of ego defensiveness. Implications for research on power, competence, and aggression are discussed.