Gerhard Johannes Paul Domagk (October 30, 1895 - April 24, 1964) was a German pathologist and bacteriologist and Nobel laureate.

Domagk was born in Lagow (Brandenburg, Germany) as son of a school headmaster. He studied medicine at the University of Kiel, but volunteered to serve as a soldier in World War I, where he was wounded in December 1914, working the rest of the war as medic. After the war, he finished his studies, and worked at the University of Greifswald, where he researched infections caused by bacteria. In 1925, he followed his professor Walter Gross to Münster. He also started working at the IG Farben laboratories at Wuppertal. The same year, he married Gertrud Strübe. Later they would have three sons and a daughter.

At IG Farben, he continued the studies of Josef Klarer and Fritz Mietzsch, based on works by Paul Ehrlich, to use dyes, at that time a major product of IG Farben, as antibiotics. He found the sulfonamide Prontosil to be effective against streptococcus, and treated his own daughter with it, saving her the amputation of an arm.

In 1939, Domagk received the Nobel Prize in Medicine for this discovery, the first drug effective against bacterial infections. He was forced by the Nazi regime to refuse the prize, after the Nazi-critical Carl von Ossietzky had won the Nobel Peace Prize in 1935. Sulfonamides became a revolutionary weapon at the time, surpassing phage therapy, but were later replaced by penicillin, which showed both better effects and fewer side effects (sulfonamides can cause kidney stones and changes in bone marrow).

After the war, in 1947, Domagk was finally able to receive his Nobel Prize. He changed his focus to tuberculosis and chemotherapy against cancer. He continued to live and work in Wuppertal. Domagk died in Burgberg (near Königsfeld, Schwarzwald).