Sorry, I cannot provide any references to support my memory. Side chains were developed by Douglas Shearer in the 30's as a continuing development of bean counters looking for a way reduce shooting costs for movies by getting rid of the sound person.
At first it was thought a compressor would even the levels so the sound person would not be required. Initial trials showed problems with sibilants. Hence the side chain. We know how effective the bean counters were at eliminating the sound person.
The odds of one the people involved with that originally, are pretty low. If they were 20 in 1935, they are now 92. Having written that, one of the founders of the AES was at the last convention in NYC. Some guy you may have heard of, Les Paul.
If my memory is correct, and it may very well not be, someone correct me.
In addition to controlling sibilants, by the sixties, sidechains were used for ducking in such hi fidelity places as department stores to reduce the music levels when "special on personal massage devices in health and beauty care!" was announced by the fully trained 17 year old, with days of experience of turning the music volume down and back.
Historically:
Andre