Axel Hugo Theodor Theorell (1903–1982) was a Swedish biochemist and Nobel Prize laureate (1955), who primarily studied enzymatic oxidation processes. He is best known for his work on cell-respiration oxidation product at the time known as ‘the yellow ferment’, myoglobin, and alcohol dehydrogenases in the liver. In 1936 he became the first director of the section for biochemisty at the newly established Medical Nobel Institute at the Karolinska Institutet (KI), and a full professor at the KI in 1959.