Linus Carl Pauling, the only person to win two unshared Nobel Prizes, revolutionized the study of chemistry, helped found the field of molecular biology, and made important advances in medical research.

Linus Pauling was born 28 February 1901 in Portland, Oregon, to a self-taught druggist, Herman Henry William Pauling, and Isabelle (Belle) Pauling, the descendent of a pioneer family. Linus received a strong blow at age nine when his father died of a perforating ulcer, leaving a wife, son, and two daughters on the edge of poverty. Belle Pauling, stunned by her husband's sudden death and disabled by pernicious anemia, spent her remaining years running a boarding house on the outskirts of Portland. Linus withdrew into books and hobbies. At age 14, a visit with a friend who owned a toy chemistry set started Pauling on his life's work. Entranced by the flames, smokes, odors, and by the sight of mysterious changes in solutions and powders, Pauling ran home and began assembling a rough "laboratory" in a corner of his basement. Here he spent his teenage years seeking order and solace in science.

During high school a sympathetic chemistry teacher recognized Pauling's talent and provided special tutoring. At age 16 Pauling dropped out to enroll at Oregon Agricultural College (now Oregon State University), intending to pursue a degree in chemical engineering.

Pauling quickly demonstrated that he knew more about chemistry than many of his professors. While still an undergraduate he was asked to teach chemistry courses in the understaffed department, an experience that gave him self-confidence--he became a great lecturer--and access to current chemical journals. Teaching these courses also gave Pauling the opportunity to meet--and later marry--Ava Helen Miller, who was enrolled in his class as part of her home economics coursework.

By the time he graduated as a chemical engineer in 1922 he had set his sights on answering one of the most important questions of chemistry: how did atoms bond together to form molecules? In order to find out, he turned from chemical engineering to chemical theory. He enrolled in the first graduate program that offered adequate support, choosing a fledgling Pasadena research school, the California Institute of Technology, or Caltech. Pauling became one of the first chemistry students in an outstanding doctoral program designed and overseen by the famed chemist Arthur Amos Noyes.

Noyes pointed Pauling in the direction of a new experimental technique called x-ray crystallography, which enabled scientists to learn about the sizes and configurations of atoms within molecules and crystals. Pauling earned his Ph.D. in 1925, and then spent 15 months in Europe on a Guggenheim Fellowship, intending to study the basics of atomic structure. His timing was propitious. A group of European physicists, including Niels Bohr, Werner Heisenberg, Wolfgang Pauli, Max Born, and Erwin Schroedinger--all of whom Pauling met--were creating new theories of atomic structure and behavior and fashioning a powerful advance in science called quantum mechanics. Pauling learned the difficult theory, as well as the mathematics that underlay it, and was one of the first to bring this important advance back to the United States. Pauling returned to Caltech in 1927 as a faculty member, and began to apply quantum mechanics to problems of chemical structure and function. His 1939 work, The Nature of the Chemical Bond, encapsulated his ideas and quickly became a standard work in the field.

At the age of 38, Pauling was a full professor and head of the chemistry division at Caltech, the youngest member ever elected to membership in the National Academy of Sciences, and the father of four children (three sons, Linus, Jr., Peter, and Crellin, and a daughter, Linda).

Pauling had started his structural studies by considering inorganic molecules, but during the 1930s he shifted his structural studies to large biomolecules, especially proteins. His biomolecular research continued through World War II, during which Pauling--an avid anti-Nazi--also developed explosives and rocket propellants. He patented an armor-piercing shell, invented an oxygen meter for submarines, and was offered the chance to head the chemistry program at the top-secret Manhattan Project-- which he turned down, not because he was averse to the idea of the atomic bomb, but because it would mean uprooting his family. After the war, his feelings towards weapons work changed when, spurred by the pacifist activism of his wife, Ava Helen, Pauling joined other scientists in calling for civilian oversight and limitations on nuclear testing. He met stiff opposition to his efforts in the charged days of the budding Cold War.

Nonetheless, his scientific research was going well. In 1949, Pauling's team discovered the molecular basis of sickle-cell anemia. He continued to work on the molecular structure of amino acids and, in the early 1950s, determined the large-scale structures of many proteins, the so-called "alpha-helix." He also worked, though unsuccessfully, on the structure of DNA. His many achievements were crowned with the awarding of the Nobel Prize in Chemistry in 1954, "for his research into the nature of the chemical bond and its application to the elucidation of the structure of complex substances."

After winning the Nobel Prize, Pauling focused his attention on peace work, organizing scientists and speaking out against nuclear testing and proliferation, often to great criticism and at remarkable personal cost. His peace activism work was capped in the fall of 1963 with the Nobel Peace Prize for 1962 (a year in which no prize had been awarded). The award was greeted with widespread criticism in the press. The lukewarm congratulations of his home institution, Caltech, led to his painful resignation from the school that had been his academic home for more than 40 years.

Pauling spent the next decade as an academic nomad, working at different think tanks and universities. For over twenty years, between 1973 and 1994, Pauling's research focused on a field he termed "orthomolecular medicine," the concept that optimal health could result from ensuring that the right molecules were present in the right amount in the body. He viewed vitamin C as one of the most important of these molecules, oversaw a number of investigations into its effects on diseases, and encouraged the ingestion of daily amounts many times greater than the accepted minimum daily requirement. Many physicians attacked his approach; the medical community criticized his decision to publish a popular book on the subject without prior peer-reviewed scientific publication; and many thought his claims unsubstantiated. Pauling fought back with typical determination. In 1973 he co-founded a California research institute devoted to the study of the health effects of vitamin C and other nutrients. He conducted research there until his death from cancer in 1994, at age 93.

Pauling's long career path led from physics to chemistry to biology to medicine. At every turn he was eager to jump disciplinary fences and explore new territory at the borders. He was attacked for his political beliefs and for going outside of accepted channels in making his results widely known. Nevertheless, in the course of his long career he wrote more than five hundred papers and eleven books, won every important prize awarded in his field, and can be considered the most significant chemist of his time.