Walter Richard Evans (January 15, 1920 – July 10, 1999) was a noted American control theorist and the inventor of the root locus method in 1948. He was the recipient of the 1987 American Society of Mechanical Engineers Rufus Oldenburger Medal and the 1988 AACC's Richard E. Bellman Control Heritage Award.
Walter Evans' principal contribution to the field of automatic control was his invention of the Evans Root Locus Method in 1948 and his subsequent invention of the Spirule, a tool used in conjunction with the root-locus method. Because it codifies very useful frequency information about a feedback system in such intuitive and appealing graphical form, Evan's root-locus method has enjoyed widespread use in the design of control systems and is now a standard chapter in texts on feedback control systems.
Evans received his B.S. in Electrical Engineering from Washington University in St. Louis, Missouri in 1941 and the M.S. degree in Electrical Engineering from the University of California at Los Angeles in 1951. During his lifetime, he worked as an engineer at several companies, including General Electric, Autonetics (then a division of North American Aviation, now known as Rockwell International), and Ford Aeronautic Company; and he also served as an instructor at Washington University for a few years.