The eponymous character of Mr. Tompkins appears in a series of books by the physicist George Gamow in which he aims to explain modern scientific theories to a popular audience.

The books are structured as a series of dreams in which Mr Tompkins enters alternate worlds where the physical constants have radically different values from those they have in the real world. This results in the counterintuitive results of relativity and quantum mechanics becoming obvious in everyday life.

Other chapters in the books deal with atomic structure and thermodynamics. In particular, Mr Tompkins makes the personal acquaintance of Maxwell's demon.