Dorothy Crowfoot Hodgkin (1910-1994) was a founder of protein crystallography. Hodgkin and her mentor, J.D. Bernal, were the first to successfully apply X-ray diffraction to biological crystals. She identified the structures of cholesterol, lactoglobulin, ferritin, tobacco mosaic virus, penicillin, and vitamin B-12. She also described the structure of insulin in 1969, a problem on which she worked for 34 years.