1930: The first documented reference to an electronic cigarette is a patent granted to Joseph Robinson in 1930 (filed in 1927). It was never commercialized and it is not entirely clear that even a prototype of this primitive device was manufactured.
1960s: Herbert A. Gilbert is generally credited with the creation of the first device that closely resembled the modern e-cigarette. He reports receiving a patent in 1965 (filed in 1963) and created prototypes (possibly never including nicotine), but failed to commercialize it. He attributes this failure the companies who might have commercialized it preferring to wait for the patent to expire rather than license it, though it is not clear whether it had commercial potential at the time.