Warburg, Otto Heinrich (1883-1970) was a German biochemist who discovered cell oxidation and the respiratory enzyme iron-oxygenase that catalyzes the process. For his work he won the 1931 Nobel Prize in physiology or medicine.

Warburg was born in 1883 in Freiburg. Germany. He earned a Ph.D. degree in chemistry from the University of Berlin in 1906, then studied medicine at the University of Heidelberg and received an M.D. degree in 1911. In 1913, he became the director of a laboratory at the Kaiser Wilhelm Institute for Biology in Berlin. During World War I (1914–1918) he served in the Prussian Horse Guards, then returned to the institute. In 1931, he became director of the Kaiser Wilhelm (later Max Planck) Institute for Cell Physiology. Warburg remained there until his death.

His early research focused on cellular respiration. Warburg discovered that carbon monoxide inhibits cell oxidation, but that specific frequencies of light counteract the effects of the carbon monoxide. He further discovered the catalyst for cellular respiration, the enzyme iron-oxygenase, and that iron was the enzyme's active ingredient. He developed a manometer (a device for measuring the pressure of gases) that measured oxygen uptake in thin slices of living tissue.

In other research, Warburg isolated several other enzymes critical to respiration and metabolism. He also studied the function of vitamins, and developed spectrophotometric methods for researching metabolism. In his studies of photosynthesis, he showed how light energy is converted to chemical energy, and discovered ferredoxin, the electron carrier in green plants.

Warburg's respiration research led to studies on how cancerous tumors grow. He discovered that instead of absorbing oxygen from the blood, cancer cells get their energy by metabolizing glucose. He believed this respiratory error was what caused the cells to become cancerous. He also believed that substances such as pesticides and artificial fertilizers inhibited oxygen uptake in cells, and advocated eating foods grown without such treatments. To fight and treat cancer, he recommended a diet rich in iron and B vitamins as sources of active respiratory enzymes.