Sir James Fraser Stoddart, FRS FRSE HonFRSC (24 May 1942 – 30 December 2024) was a British-American chemist who was Chair Professor in Chemistry at the University of Hong Kong. He was the Board of Trustees Professor of Chemistry and head of the Stoddart Mechanostereochemistry Group in the Department of Chemistry at Northwestern University in the United States. He worked in the area of supramolecular chemistry and nanotechnology. Stoddart developed highly efficient syntheses of mechanically-interlocked molecular architectures such as molecular Borromean rings, catenanes and rotaxanes utilising molecular recognition and molecular self-assembly processes. He demonstrated that these topologies can be employed as molecular switches. His group has even applied these structures in the fabrication of nanoelectronic devices and nanoelectromechanical systems (NEMS). His efforts were recognized by numerous awards, including the 2007 King Faisal International Prize in Science. He shared the Nobel Prize in Chemistry together with Ben Feringa and Jean-Pierre Sauvage in 2016 for the design and synthesis of molecular machines.

Fraser Stoddart was born in Edinburgh, Scotland, on 24 May 1942, the only child of Tom and Jean Stoddart. He was brought up as a tenant farmer on Edgelaw Farm, a small community consisting of three families. Sir Fraser professed a passion for jigsaw puzzles and construction toys in his formative years, which he believed was the basis for his interest in molecular construction.

Stoddart received early schooling at the local village school in Carrington, Midlothian, before going on to Melville College in Edinburgh. He started at the University of Edinburgh in 1960 where he initially studied chemistry, physics and mathematics. He was awarded a Bachelor of Science degree in Chemistry in 1964 followed by a Doctor of Philosophy in 1966 for research on natural gums in Acacias supervised by Sir Edmund Langley Hirst and D M W Anderson from the University of Edinburgh.

In 1967, Stoddart went to Queen's University (Canada) as a National Research Council Postdoctoral Fellow. In 1970 he moved to the University of Sheffield as an Imperial Chemical Industries (ICI) Research Fellow, before joining the academic staff as a lecturer in chemistry. In early 1978 he was a Science Research Council Senior Visiting Fellow at the University of California, Los Angeles (UCLA) Department of Chemistry and Biochemistry. Later in 1978, he was transferred to the ICI Corporate Laboratory in Runcorn, England where he first started investigating the mechanically interlocked molecules that would eventually become molecular machines. At the end of the three year secondment he returned to Sheffield where he was promoted to a Readership in 1982.

Stoddart was awarded a Doctor of Science degree from the University of Edinburgh in 1980 for his research into stereochemistry beyond the molecule. In 1990, he moved to the Chair of Organic Chemistry at the University of Birmingham and was Head of the School of Chemistry there (1993–97) before moving to UCLA as the Saul Winstein Professor of Chemistry in 1997, succeeding Nobel laureate Donald Cram.

In July 2002, Stoddart became the Acting Co-Director of the California NanoSystems Institute (CNSI). In May 2003, he became the Fred Kavli Chair of NanoSystems Sciences and served from then through August 2007 as the Director of the CNSI.

In 2008, Stoddart established the Mechanostereochemistry Group and was named Board of Trustees Professor in Chemistry at Northwestern University. He went on to be the Director of the Center for the Chemistry of Integrated Systems (CCIS) at Northwestern University in 2010.

In 2017, Stoddart was appointed a part-time position at the University of New South Wales to establish his New Chemistry initiative at the UNSW School of Chemistry.