David Harker

David Harker (October 19, 1906 – February 27, 1991) was an American medical researcher who according to The New York Times was "a pioneer in the use of X-rays to decipher the structure of critical substances in the life process of cells".

He is also well known for Harker–Kasper inequalities (statistical relationships between the phases of structure factors), which he devised in collaboration with John S. Kasper.

His lab solved the structure of the pancreatic enzyme ribonuclease A, the third protein structure ever solved by protein crystallography. Harker was a member of the National Academy of Sciences, and the head of the crystallography division of General Electric. After retirement from Roswell Park in 1976, he joined the Hauptman-Woodward Medical Research Institute (HWI), then known as the Medical Foundation of Buffalo. He remained there until he died in 1991. His research interests while at HWI turned towards mathematical aspects of crystallography, including magnetic space groups and infinite polyhedra.