Hawking’s work, The Universe in a Nutshell, is a work of nonfiction, chronicling history and the attempts of both the author and various other theoretical physicists to reconcile numerous scientific principles into one cohesive idea. Therefore, the characters mentioned are real individuals. Further, Hawking spends little time on the theorists themselves and much more time on the ideas presented in the work.

Albert Einstein

Einstein is clearly a very famous individual, one of the most renowned in the history of science. His contributions to the world of science were world-shattering, as they overthrew conventional knowledge that had been firmly established for several hundred years, challenging our knowledge of gravity and time themselves. Much of the work done by Hawking and his colleagues was to reconcile Einstein’s ideas with other radical yet also experimentally verified concepts, namely quantum mechanics and quantum electrodynamics.

Richard Feynman

Feynman is sometimes referred to as a "rock star" of the physics world. A much more cavalier and charming individual than other scientists, he is noted for his work both on the Manhattan Project and later in the development of quantum electrodynamics, which reconciled the foundations of quantum mechanics with observable phenomena relating to all particles, not just electrons and protons. His development of so-called Feynman Diagrams revolutionized the conceptualization of particle interactions and has become a standard in most discussions of particle physics.

Kurt Gödel

Kurt Gödel was a mathematician who occasionally dabbled in physics. The concepts of interest from him, however, are his rules of systematic logic, namely the Theory of Incompleteness. Hawking spends a great deal of time on the Theory of Incompleteness and how it pertains to quantum mechanics.

Erwin Schrodinger

Schrodinger is a name just as likely to turn up in a psychology textbook as a Physics one for his famous thought experiment known as Schrodinger’s Cat. This experiment, alongside his other work in the field of Physics, earned him the label "The Father of Quantum Mechanics." It is primarily his famous equation regarding the probabilistic motion of particles, which is fundamental to the understanding of quantum phenomena, that is being reconciled with Einstein’s Theory of Relativity.