The book explores the creation of digital personalities that mimic human behaviour and cognition, authored by AI and computer science experts. It covers the technical foundations needed to develop advanced digital personas, focusing on the integration of ontologies, natural language processing (NLP), and dialogue generation. Ontologies are highlighted for their role in structuring knowledge, while NLP techniques are explored for enabling human-like dialogue. The book examines algorithms for sentiment analysis, entity recognition, and context understanding. Dialogue generation is also discussed, from rule-based methods to deep learning, emphasizing seamless user interactions. Ethical concerns, such as privacy, bias, and accountability, are addressed, advocating for responsible AI practices. This volume is a comprehensive resource for researchers and enthusiasts, offering both theoretical insights and practical guidance on building lifelike digital entities and fostering emotionally engaging human-computer interactions.