Josiah Willard Gibbs was an influential American physicist, chemist, and mathematician known for his groundbreaking contributions to thermodynamics and physical chemistry. His work laid the foundation for understanding microstates, macrostates, and ensemble averages, particularly through the development of concepts such as chemical potential and Gibbs free energy. Gibbs' formulations help connect the microscopic behavior of particles with macroscopic thermodynamic properties, which are essential for analyzing systems in statistical mechanics.