William Ritt was an American mathematician known for his contributions to the field of mathematics, particularly in the area of mathematical logic. He is recognized for his work on formal systems and proof theory, which are essential for understanding the foundations of mathematics. Ritt also made significant advancements in differential algebra, a branch of mathematics that studies algebraic structures related to differential equations. His research has influenced various areas of mathematics and has been foundational for later developments in both algebra and calculus.