Allan MacLeod Cormack (February 23, 1924 – May 7, 1998) was a South African American physicist and Professor of Physics at Tufts University who won the 1979 Nobel Prize in Physiology or Medicine (along with Godfrey Hounsfield) for his work on X-ray computed tomography (CT), a significant and unusual achievement since Cormack did not hold a doctoral degree in any scientific field.

Following a sabbatical at Harvard in 1956–57, the couple agreed to move to the United States, and Cormack became a professor at Tufts University in the fall of 1957.

Although he was mainly working on particle physics, Cormack's side interest in x-ray technology led him to develop the theoretical underpinnings of CT scanning.

This work was initiated at the University of Cape Town and Groote Schuur Hospital in early 1956 and continued briefly in mid-1957 after returning from his sabbatical.

These papers generated little interest until Hounsfield and colleagues built the first CT scanner in 1971, taking Cormack's theoretical calculations into a real application.