Tristan Needham is the author of the highly original book "Visual Complex Analysis" (Oxford, 1997) in which he uses a geometric approach to develop complex analysis (which he says was inspired by Isaac Newton's original geometric approach to ordinary calculus). He was a student of Roger Penrose and is currently a professor of mathematics at the University of San Francisco. Complex analysis is the branch of mathematics investigating functions of complex numbers, and is of enormous practical use in many branches of mathematics, including applied mathematics. ... Sir Isaac Newton, FRS (4 January 1643 – 31 March 1727) [OS: 25 December 1642 – 20 March 1727][1] was an English physicist, mathematician, astronomer, alchemist, and natural philosopher, widely regarded as one of the key figures in the history of science. ... Calculus is a central branch of mathematics. ... Sir Roger Penrose, OM, FRS (born 8 August 1931) is an English mathematical physicist and Emeritus Rouse Ball Professor of Mathematics at the University of Oxford and Emeritus Fellow of Wadham College. ...