Hi,
Ernst Alexanderson of GE held the controlling TRF patent, on the
principle of inserting tuned circuits between successive gain stages.
It was a rather obvious concept but as just noted, everything was
patentable in those days. Interestingly, Sparton got around
Alexanderson's patent by putting all the tuning at the front end,
feeding a series of untuned RF stages.

Wikipedia is wrong. Howard Armstrong was indeed working on the
superheterodyne in 1918:

http://antiqueradios.com/superhet/

(loading is apt to be slow, since the server also handles an active
antique-radio forum).

73, Alan