Otto Knut Olof Folin (April 4, 1867 – October 25, 1934) was a Swedish-born American chemist who is best known for his groundbreaking work at Harvard University on practical micromethods for the determination of the constituents of protein-free blood filtrates and the discovery of creatine phosphate in muscles.

[3] In 1896, Folin returned to Sweden and began his research in the laboratory of Prof. Olof Hammarsten (1841-1932) at Uppsala University.

He moved to the McLean Hospital Boston in 1900 as a research biochemist, eventually moving to Harvard Medical School in 1907 as an associate professor of biological chemistry, becoming the Hamilton Kuhn Professor of Biological Chemistry and Molecular Pharmacology in 1909.

In 1920, he co-developed with Hsien Wu the Folin-Wu method of assaying glucose in protein-free filtrates of blood.

He was elected to the National Academy of Sciences and was awarded the Carl Wilhelm Scheele Medal of the Swedish Chemical Society in 1930.