Linus Carl Pauling (; February 28, 1901 - August 19, 1994) was an American chemist, biochemist, peace activist, author, educator, and husband of American human rights activist Ava Helen Pauling. He published more than 1,200 papers and books, of which about 850 dealt with scientific topics. New Scientist called him one of the 20 greatest scientists of all time, and as of 2000, he was rated the 16th most important scientist in history. Pauling was one of the founders of the fields of quantum chemistry and molecular biology.

Pauling's discoveries led to decisive contributions in a diverse array of areas including around 350 publications in the fields of quantum mechanics, inorganic chemistry, organic chemistry, protein structure, molecular biology, and medicine.  His work on chemical bonding marks him as one of the founders of modern quantum chemistry. The Nature of the Chemical Bond was the standard work for many years, and concepts like hybridization and electronegativity remain part of standard chemistry textbooks. While his Valence bond approach fell short of accounting quantitatively for some of the characteristics of molecules, such as the color of organometallic complexes, and would later be eclipsed by the molecular orbital theory of Robert Mulliken, Valence Bond Theory still competes, in its modern form, with Molecular Orbital Theory and density functional theory (DFT) as a way of describing the chemical phenomena. Pauling's work on crystal structure contributed significantly to the prediction and elucidation of the structures of complex minerals and compounds. His discovery of the alpha helix and beta sheet is a fundamental foundation for the study of protein structure.  Francis Crick acknowledged Pauling as the "father of molecular biology". His discovery of sickle cell anemia as a "molecular disease" opened the way toward examining genetically acquired mutations at a molecular level.  Pauling's 1951 publication with Robert B. Corey and H. R. Branson, "The Structure of Proteins: Two Hydrogen-Bonded Helical Configurations of the Polypeptide Chain," was a key early finding in the then newly emerging field of molecular biology. This publication was honored by a Citation for Chemical Breakthrough Award from the Division of History of Chemistry of the American Chemical Society presented to the Department of Chemistry, Caltech, in 2017.

What other important discoveries did he make?
His discovery of the alpha helix and beta sheet is a fundamental foundation for the study of protein structure.