This paper is a primer exploring the concept of intelligence, which underpins life and artificial intelligence. As machine learning-based AI already significantly impacts our lives, this paper explores various aspects of essential intelligence to understand the possibilities and limitations of future systems. Intelligence is not a single measurable quantity; it encompasses diverse academic disciplines such as biology, physics, philosophy, cognitive science, neuroscience, psychology, and computer science. It emphasizes that future engineers and scientists must broaden their understanding of fields like psychology, philosophy, and ethics. The emergence of artificial intelligence and its legal requirements serve as a driving force for bringing these broad topics to the forefront. This paper begins with an introduction to intelligence and progresses to deeper concepts and ideas, aiming to help readers shape their future and raise new questions.