Generalized second law of thermodynamics in black-hole physics.

In "PHYSICAL REVIEW D PARTICLE AND FIELDS", Third series, vol. 9, N. 12, 15 june 1974, pp.3292-3300, the entire issue in original printed wrappers. Light stamp with cancellation sign on front cover, a fine copy. First edition.
"In 1972, Bekenstein was the first to suggest that black holes should have a well-defined entropy. He wrote that a black hole's entropy was proportional to the area of its (the black hole's) event horizon. Bekenstein also formulated the generalized second law of thermodynamics, black hole thermodynamics, for systems including black holes. Both contributions were affirmed when Stephen Hawking (and, independently, Zeldovich and others) proposed the existence of Hawking radiation two years later. Hawking had initially opposed Bekenstein's idea on the grounds that a black hole could not radiate energy and therefore could not have entropy.However, in 1974, Hawking performed a lengthy calculation that convinced him that particles can indeed be emitted from black holes. Today this is known as Hawking radiation. Bekenstein's doctoral adviser, John Archibald Wheeler, also worked with him to develop the no-hair theorem, a reference to Wheeler's saying that "black holes have no hair," in the early 1970s. Bekenstein was the first physicist to postulate such a theorem. His suggestion was proven to be unstable, but it was influential in the development of the field.
Based on his black-hole thermodynamics work, Bekenstein also demonstrated the Bekenstein bound: there is a maximum to the amount of information that can potentially be stored in a given finite region of space which has a finite amount of energy (which is similar to the holographic principle).
In 1982, Bekenstein was the first person to develop a rigorous framework to generalize the laws of electromagnetism to handle inconstant physical constants. His framework replaces the fine-structure constant by a scalar field. However, this framework for changing constants did not incorporate gravity.
In 2004, Bekenstein greatly boosted Mordehai Milgrom's theory of Modified Newtonian Dynamics (MOND) by developing a relativistic version. It is known as TeVeS for Tensor/Vector/Scalar and it introduces three different fields in space time to replace the one gravitational field." (https://en.wikipedia.org/wiki/Jacob_Bekenstein).