Major Walter Reed, M.D., (September 13, 1851 – November 23, 1902) was a U.S. Army physician who in 1900 led the team which postulated and confirmed the theory that yellow fever is transmitted by mosquitoes, rather than by direct contact. This insight gave impetus to the new fields of epidemiology and biomedicine and most immediately allowed the resumption and completion of work on the Panama Canal (1904–14) by the United States.

Walter Reed was born in Belroi, Virginia and moved to Lebanon, Missouri, an unincorporated community in Laclede County, to Lemuel Sutton Reed (a Methodist minister) and Pharaba White.

After two year-long classes at the University of Virginia, Reed completed the M.D. degree in 1869, at the age of 18. He then enrolled at the New York University's Bellevue Hospital Medical College in Manhattan, New York, where he obtained a second M.D. in 1870. After interning at several New York City hospitals, he worked for the New York Board of Health until 1875. He married Emilie (born Emily) Lawrence on April 26, 1876 and took her west with him. Later, Emilie would give birth to a son and a daughter and the couple would adopt an Indian girl while posted in frontier camps.