We tested the hypothesis that proactivity represents the engagement vector in the HEXACO model of personality. Questionnaire data were obtained in five studies, three of which consisted (mostly) of students: Study 1 (N = 188, Mage = 20.0, 89.4% women), Study 3 (N = 315, Mage = 20.4, 80.6% women), and Study 4 (N = 309 self-ratings, Mage = 20.0, 78.3% women; N = 307 other-ratings, Mage = 24.5, 62.2% women). Participants in the other two studies came from an ISO-certified representative community panel: Study 2 (N = 525, Mage = 51.2, 52.0% women) and Study 5 (N = 736, Mage = 42.2, 48.0% women). Proactive Personality and Proactivity were positively related to Extraversion, Conscientiousness, and Openness to Experience, but only weakly related or unrelated to Honesty-Humility, Emotionality, and Agreeableness, supporting the alignment of Proactive Personality/Proactivity with the hypothesized HEXACO engagement vector. Additionally, Proactivity explained incremental variance in self-rated job performance on top of the HEXACO facets that were most closely associated with Proactive Personality/Proactivity, that is, Social Boldness (an Extraversion facet), Diligence (a Conscientiousness facet), and Creativity (an Openness to Experience facet), but not in entrepreneurship and intrapreneurship. Proactivity is the missing engagement link in the HEXACO model of personality. The results are discussed in light of higher-order factors (e.g., general factor of personality and Alpha and Beta) of personality and bandwidth-fidelity controversies.