Coining the term Penguin diagram[3] Jonathan Richard "John" Ellis CBE FRS HonFInstP (born 1 July 1946[6]) is a British-Swiss theoretical physicist.

After completing his secondary education at Highgate School, he attended King's College, Cambridge from 1964, earning his PhD in theoretical (high-energy) particle physics in 1971, after having spent the academic year 1970/71 as a visiting student at CERN.

[7] After one-year post-doc positions in the SLAC Theory Group[8] and at Caltech,[9] he went back to CERN in 1973, first as a research fellow and from 1974 as a staff member,[10] where he remained until he reached the fixed retirement age of 65.

[11] Since 2010 Ellis is Clerk Maxwell Professor of Theoretical Physics at King's College London, but continues to work at CERN holding a visiting scientist appointment.

[21] Ellis' research interests focus on the phenomenological aspects of particle physics, and he has also made important contributions to astrophysics, cosmology and quantum gravity.

[29] Ellis and collaborators later pioneered the analysis of so-called "benchmark scenarios" meant to illustrate the range of phenomenology to be expected from supersymmetric models;[30] such analyses have played a major role in evaluating the promise of various future accelerator options.

[35][36] Ellis has subsequently been one of the leading opponents of the Standard Model Effective Field Theory as a technique for analyzing Higgs and other relevant data from the LHC and elsewhere.

Naturally his theoretical work reflected these connections, as when he showed that data from the Stanford Linear Collider (SLC) and from LEP could be used to predict the masses of the top quark and the Higgs boson.

In the context of the LHC, he has interacted frequently with physicists, administrators at universities and institutes, and ministers of funding agencies and diplomatic corps from a wide variety of countries, ranging from major CERN partners like the United States, Russia, Japan, Canada, India, Israel, Armenia and China, to states with nascent physics programs such as Azerbaijan, the Baltic republics, Bolivia, Colombia, Croatia, Cyprus, Iran, Madagascar, New Zealand, Pakistan, Romania, Sri Lanka, Vietnam, Palestine, Rwanda, and others.