Original: Marshall is well-known for proving that the bacterium Helicobacter pylori is the cause of most peptic ulcers , reversing decades of medical doctrine which held that ulcers were caused by stress , spicy foods , and too much acid .
Simplified: Barry James Marshall , AC , FRS , FAA ( born 30 September 1951 ) is an Australian doctor and winner of the 2005 Nobel Prize in Physiology or Medicine .