Many negatively connoted personality traits (often termed "dark traits") have been introduced to account for ethically, morally, and socially questionable behavior. Herein, we provide a unifying, comprehensive theoretical framework for understanding dark personality in terms of a general dispositional tendency of which dark traits arise as specific manifestations. That is, we theoretically specify the common core of dark traits, which we call the Dark Factor of Personality (D). The fluid concept of D captures individual differences in the tendency to maximize one's individual utility- disregarding, accepting, or malevolently provoking disutility for others-accompanied by beliefs that serve as justifications. To critically test D, we unify and extend prior work methodologically and empirically by considering a large number of dark traits simultaneously, using statistical approaches tailored to capture both the common core and the unique content of dark traits, and testing the predictive validity of both D and the unique content of dark traits with respect to diverse criteria including fully consequential and incentive-compatible behavior. In a series of four studies (N > 2,500), we provide evidence in support of the theoretical conceptualization of D, show that dark traits can be understood as specific manifestations of D, demonstrate that D predicts a multitude of criteria in the realm of ethically, morally, and socially questionable behavior, and illustrate that D does not depend on any particular indicator variable included.