Which bacterium causes peptic ulcers? Who discovered the above pathogen for the first time?

Peptic ulcer disease (PUD) is a break in the lining of the stomach, first part of the small intestine or occasionally the lower esophagus.

Helicobacter pylori, is a gram-negative bacteria found in stomach is known to cause peptic ulcers. Barry J Marshall and Robin Warren discovered this bacteria for the first time.

Note- They got Nobel Prize for this discovery in year 2005.