Barry J. Marshall, M.D. is an Australian doctor and Professor of Clinical Microbiology at the University of Western Australia. He is well-known for proving that the bacteria Helicobacter pylori is the cause of most stomach ulcers, reversing decades of medical doctrine which held that ulcers were caused by stress, spicy foods, and too much acid.

The H. pylori theory was ridiculed by the establishment scientists and doctors, who did not believe that any bacteria could live in the acidic stomach. To force people to pay attention to this theory, Marshall drank a test tube of the bacteria and soon developed gastric ulcers, which he then cured by antibiotics.