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

The bacterium that causes peptic ulcers is: Helicobacter pylori.

The scientists Marshall and Warren discovered this bacterium is the year 1982 after they diagnosed that these germs caused the stomach ulcers*.

*Ulcer: It is an open sore in the internal surface of the body caused by the breaking of the skin.