Biography of Howard Aiken, a major figure of the early digital era, by a major historian of science who was also a colleague of Aiken's at Harvard. Howard Hathaway Aiken (1900-1973) was a major figure of the early digital era. He is best known for his first machine, the IBM Automatic Sequence Controlled Calculator or Harvard Mark I, conceived in 1937 and put into operation in 1944. But he also made significant contributions to the development of applications for the new machines and to the creation of a university curriculum for computer science. This biography of Aiken, by a major historian of science who was also a colleague of Aiken's at Harvard, offers a clear and often entertaining introduction to Aiken and his times. Aiken's Mark I was the most intensely used of the early large-scale, general-purpose automatic digital computers, and it had a significant impact on the machines that followed. Aiken also proselytized for the computer among scientists, scholars, and businesspeople and explored novel applications in data processing, automatic billing, and production control. But his most lasting contribution may have been the students who received degrees under him and then took prominent positions in academia and industry. I. Bernard Cohen argues convincingly for Aiken's significance as a shaper of the computer world in which we now live.