In the 1940's, Erwin Müller dominated field emission research. The 50's and 60's saw considerable growth in the number of scientists interested in field emission. While many made important contributions, three persons stood out who had different talents and interests. First and foremost: Erwin Müller, a very innovative, creative and skilled inventor and experimentalist. Second: Robert Gomer, equally adept at theory and experiment, with a unique mastery of fundamental physics concepts. Third: Walter Dyke, who was intrigued by the unique properties of field emission and resolved to develop field emission cathodes as high performance electron sources for a variety of electron beam devices. This paper summarizes Dyke's work at Linfield College, Linfield Research Institute and Field Emission Corporation from 1948 to 1972. However, while Dyke established a solid foundation for useful field emission cathodes and investigated several devices, particularly in microwaves, electron optics and flash radiography, he was unable to complete his work and produce commercial devices, except for flash radiography. Many groups have pursued this work in recent years, sometimes with great success. This paper briefly summarizes current work on field emission cathodes and device applications, as this puts Dyke's work in better perspective and adds to its significance.