Sir Chris Llewellyn Smith chats to Jim Al-Khalili about quarks, bosons, and running the biggest experiments in history.

In the late 60s and early 70s Chris was one of the theoretical physicists who were busy sketching what would become known as the standard model of particle physics. An early believer in the physical reality of the "Quark Model", Chris's work helped confirm that the protons and neutrons at the centre of atoms are themselves made up of 3 quarks.

He was also influential in showing that Peter Higgs' theory of mass was not just sufficient, but also necessary.

So when later he was made Director General of CERN, he was well placed to know, and to explain to the heads of the member states, that investing in the construction of something called the Large Hadron Collider would be a scientifically fruitful thing to do. Indeed, it has been said that there would be no LHC without Chris' calm international scientific diplomacy.

Since then, Chris has been influential in several other international big-physics collaborations, including the world's most ambitious nuclear fusion programme, ITER.