Frank H. Krusen, MD, was arguably the most influential member of the small group of physicians who began in 1938 a long and difficult struggle to win acceptance of physical medicine and rehabilitation as a medical specialty. The struggle was aided immeasurably in 1943 when a millionaire philanthropist, M. Bernard Baruch, financed the establishment of the Baruch Committee on Physical Medicine. Dr. Krusen became the Director-Secretary of the Committee and began to keep a daily diary in which he recorded his activities and those of his colleagues in their quest for recognition of PM&R as a specialized field of medical practice. That recognition came in 1947 with the establishment of the American Board of Physical Medicine, but Dr. Krusen continued his diary through 1967. In 1988, 15 years after his death, Dr. Krusen's family donated a copy of the diary to the History of Medicine Library of the Mayo Clinic in Rochester, MN. The gift coincided with the American Academy of Physical Medicine and Rehabilitation's celebration of its 50th anniversary. This article, the first of four, introduces the reader to Dr. Krusen and describes his early years and his professional development in the years before 1943.