J. Theodorsen was an American engineer and researcher known for his contributions to aerodynamics and fluid dynamics. He is particularly recognized for his work on the theory of lifting surfaces, which has applications in the design of aircraft and other vehicles. His research helped improve the understanding of how air interacts with solid objects, leading to advancements in aviation technology. Theodorsen is also known for the Theodorsen function, a mathematical tool used in the analysis of unsteady aerodynamic forces. This function plays a crucial role in predicting the behavior of wings and other surfaces in motion through air, making it essential for engineers and scientists in the field of aeronautics.