Who developed the foundational theories of probability?

The foundational theories of probability were significantly developed by Blaise Pascal, often in collaboration with Pierre de Fermat. Their correspondence in the 17th century laid the groundwork for the mathematical field of probability, particularly through their discussions on games of chance and the principles governing such calculations. Pascal's contributions, especially in formulating questions related to expected value, risk assessment, and decision-making under uncertainty, were critical to the establishment of probability theory as a formal discipline. Although Pierre de Fermat also played a crucial role in this development, it is Pascal’s work and influence that are frequently recognized as pivotal in the initial formulation of probability concepts.