Internationalization decisions stand as a cornerstone of research in the field of international business. Scholars have dedicated nearly five decades to examining the role of decision-makers, specifically strategic actors, in shaping the internationalization strategies of firms. Unlike previous research that primarily examines the relationships and connections decision-makers possess, such as social capital, and their specific knowledge, such as international expertise, this dissertation aims to explore the intricacies of the decision-makers themselves. Who are these influential figures steering firms toward international growth? How do their characteristics shape and drive the internationalization process? This approach aims to bridge the existing gap in the literature by offering a fresh perspective on the personal dimensions of internationalization decision-makers. Specifically, this research examines the understudied realm of Chief Executive Officers’ (CEOs’) characteristics, with a particular focus on the dark triad of personality traits, shedding light on how these traits affect CEOs’ decisions in the complex landscape of international business. The dark triad personality encompasses narcissism, psychopathy, and Machiavellianism, which are known to have both positive and negative implications in various organizational contexts. This research, grounded in the upper echelons theory and dynamic capabilities view, examines the CEO's dark triad personality and its influence on a firm's internationalization outcomes. First, focusing on the upper echelons theory, which suggests the influence of CEOs’ characteristics on firm-level outcomes, the research explores the direct effects of dark triad personality traits on a firm’s degree of internationalization and ambidexterity. Second, focusing on the dynamic capabilities view, the research examines the indirect effects mediated through ambidexterity, characterized by the pursuit of both exploration and exploitation. Cultivating a firm’s dynamic capabilities to navigate complex international markets effectively necessitates a balance between exploitation and exploration. This research comprises two studies aimed at examining the aforementioned relationships. Study 1 focuses on CEOs of firms in the United Kingdom and the United States, with data collected through the Prolific platform. The second study aims to extend the findings of the first study by testing the same hypotheses in a similar cultural context. Conducting a second study can help replicate and validate the findings of the first study, thereby increasing the explanatory power and generalizability of the results. Study 2 encompasses CEOs from Ireland, the United Kingdom, and Australia. For this study, data were collected by emailing CEOs and inviting them to participate, with the majority of participants being from Ireland, with a smaller representation from the United Kingdom and Australia. Both Studies 1 and 2 utilize a quantitative research approach, analyzing survey data to examine the proposed relationships. In Study 1, the results of hypothesis testing provided support for all four hypotheses. Firstly, it was found that there is a positive and significant relationship between the CEO's dark triad personality and a firm's degree of internationalization. Secondly, the study showed a positive and significant relationship between the CEO’s dark triad personality and ambidexterity. Thirdly, the study demonstrated a positive and significant relationship between ambidexterity and a firm's degree of internationalization. Lastly, ambidexterity was found to mediate the relationship between the CEO's dark triad personality and a firm's degree of internationalization. The results of Study 2 fail to substantiate the direct relationship between the CEO's dark triad personality and a firm’s degree of internationalization. While Study 2 did establish a positive and significant connection between ambidexterity and the degree of internationalization, it did not find a significant relationship between the CEO's dark triad personality and ambidexterity. In contrast to Study 1, ambidexterity does not mediate the relationship between the CEO's dark triad personality and a firm's degree of internationalization. However, further examination of Study 2 revealed that dark triad CEOs tend to prioritize and engage in exploitation activities initially. Subsequently, these CEOs are more likely to engage in exploration activities, which in turn contribute to enhancing the firm's degree of internationalization. The findings of this dissertation have several research and practical implications. Theoretically, they contribute to understanding how CEO dark triad personality traits shape firm internationalization behaviors, shedding light on the interplay between individual characteristics, ambidexterity, and firm-level outcomes. The research also extends the literature on the intersection of upper echelons theory and dynamic capabilities in the context of international business. Practically, the dissertation offers valuable insights for practitioners and decision-makers involved in international business operations. By recognizing the potential positive aspects of a CEO's dark triad personality, firms can strategically leverage specific traits. These traits include assertiveness, self-confidence, boldness, risk-taking, and strategic thinking. Such characteristics may help firms navigate complex international environments, foster innovation, and seize opportunities for growth and expansion. Moreover, the findings highlight the importance of fostering exploitation and exploration (ambidextrous) capabilities within small firms. Overall, the findings of this research present opportunities for future studies to expand upon and develop existing knowledge.