Richard S. Westfall  is best known for his biography of a mathematician who was a key figure in what?
Isaac Newton Sir Isaac Newton {'1': ", '2': ", '3': ", '4': "} ( ; 25 December 1642 – 20 March 1726/27) was an English mathematician, astronomer, and physicist (described in his own day as a "natural philosopher") who is widely recognised as one of the most influential scientists of all time and a key figure in the scientific revolution. His book "Philosophiæ Naturalis Principia Mathematica" ("Mathematical Principles of Natural Philosophy"), first published in 1687, laid the foundations of classical mechanics. Newton also made pathbreaking contributions to optics, and he shares credit with Gottfried Wilhelm Leibniz for developing the infinitesimal calculus.
Richard S. Varga Richard Steven Varga ( ; born October 9, 1928) is an American mathematician who specializes in numerical analysis and linear algebra. He is currently an Emeritus University Professor of Mathematical Sciences at Kent State University and an adjunct Professor at Case Western Reserve University. Varga is known for his contributions to many areas of mathematics, including matrix analysis, complex analysis, approximation theory, and scientific computation. He is the author of the classic textbook "Matrix Iterative Analysis". Varga has been the Editor-in-Chief of the journal "Electronic Transactions on Numerical Analysis" (ETNA).