This paper introduces an innovative approach to enhancing user engagement in health and wellness chatbots through the implementation of personality-driven AI design. By leveraging advanced Large Language Models (LLMs) and principles of human-centered design, we developed a web-based chat solution featuring distinct AI personas. The system was deployed as a consumer-focused product, engaging thousands of users over several weeks. Our findings demonstrate significantly higher user engagement compared to traditional chatbot interactions, with extended conversation durations and improved user retention. The personality-driven approach led to more natural, compelling interactions, potentially increasing the effectiveness of digital health interventions. This study provides valuable insights into the potential of human-centered AI design in creating more engaging and impactful health and wellness tools. Moreover, it raises important considerations about the ethical implications and long-term effects of highly engaging AI interactions in healthcare contexts. Our research contributes to the growing body of knowledge on AI applications in digital health, offering a novel perspective on how personality-driven chatbots can transform user experiences in health and wellness platforms.