Opinion leadership as a measure of individual differences describes influential individuals who informally shape the attitudes and behaviors of their peers. It is commonly assumed that the most important source of opinion leadership stems from expert knowledge in their domain of influence. Study 1 (N= 183), however, demonstrates that objective knowledge does not predict opinion leadership unambiguously. Rather, the relationship is moderated by a personality trait measuring stable dispositions for social influence, thus highlighting two different roots of opinion leadership: domain-specific competencies and domain-independent traits. Furthermore, Study 2 on N= 185 pairs of acquaintances illustrates that the interaction effect of these two sources on other-reports of opinion leadership is mediated by the degree of word-of-mouth communication.