The date of the first application of a pickup to a guitar is
uncertain but Loyd Loar who worked for Gibson from 1920 to 1924
(and is famous for his mandolins and arch tops) developed a
pickup. The company developed a bunch of prototypes which were
not accepted by the "agents" (who I believe sold to the
retailers). Vivi-Tone was founded by Loar and two other folks
from Gibson - however they were too far ahead of the curve and
there was no market. Walter Fuller recalled that when he joined
Gibson in 1933, he found some pickups that he believed were made
ten years earlier under Loar's supervision. They were more like
microphones than modern day pickups with a fixed anode and a
charged, stretched diaphragm. It was not a successful design.
Commercially successful electric instruments began to appear in
the 1930s. In 1931 Rickenbacher (that's a correct spelling for
the era) produced a Hawaiian guitar that came to be known as the
"Frying Pan". It was the first instrument to use a modern style
electromagnetic pickup