Leslie Eleazer Orgel FRS[1] (12 January 1927 – 27 October 2007) was a British chemist and member of the National Academy of Sciences, known for his theories on the origin of life.

Orgel started his career as a theoretical inorganic chemist and continued his studies in this field at Oxford, the California Institute of Technology, and the University of Chicago.

Together with Sydney Brenner, Jack Dunitz, Dorothy Hodgkin, and Beryl M. Oughton he was one of the first people in April 1953 to see the model of the structure of DNA, constructed by Francis Crick and James Watson, at the time he and the other scientists were working at Oxford University's Chemistry Department.

Orgel formulated his protein-translation error-catastrophe theory of aging in 1963,[4] (prior to the use of the term by Manfred Eigen for mutational error catastrophe) which has since been experimentally challenged.

[5] In 1964, Orgel was appointed senior fellow and research professor at the Salk Institute for Biological Studies in La Jolla, California, where he directed the Chemical Evolution Laboratory.

He was also an adjunct professor in the Department of Chemistry and Biochemistry at the University of California, San Diego, and he was one of five principal investigators in the NASA-sponsored NSCORT program in exobiology.

"[6] In his book The Origins of Life, Orgel coined the concept of specified complexity, to describe the criterion by which living organisms are distinguished from non-living matter.

Conference at Trinity College in Dublin, Ireland along with many other prominent scientists exploring the origin of life research such as Manfred Eigen, John Maynard Smith and Stephen Jay Gould.

Continuing his work studying the prebiotic synthesis of RNA, Orgel explored mechanisms by which inorganic phosphate[10] and nucleotide phosphoryl groups[11] could be chemically activated for condensation into nucleic acid polymers.

Montmorillonite clay was also shown to promote the polymerization of adenosine phosphorimidazolide into oligonucleotides tens of bases in length starting from a poly-adenosine 10-mer primer.