Paul Karrer was a Russian-born Swiss chemist who shared the 1937 Nobel Prize in Chemistry with Walter Haworth for research on coenzymes, carotenoids, and vitamins. In 1930 Karrer determined the formula of beta carotene, the precursor of vitamin A, and in 1931 elucidated the structure of the vitamin itself. He also studied vitamin E and demonstrated that lactoflavin was a part of the vitamin B₂ complex.