Short answers, pulled from the story.
Ken Townsend was an English sound engineer who spent his entire working career at EMI, playing a key role at what became Abbey Road Studios. He worked with the Beatles throughout their time at EMI and retired as Chairman of the Studio Group in 1995.
In 1966, Ken Townsend invented artificial double tracking, known as ADT. He built it by taking the signal from the playback and recording heads and delaying it slightly to create two sound images from one original signal.
Ken Townsend was hired as a recording engineer at EMI Studios in 1954, after a four-year apprenticeship at EMI's Hayes facility.
Ken Townsend created automatic double tracking because John Lennon complained about always having to do a second take to double his vocals. The complaint came up during the recording of "Tomorrow Never Knows."
Ken Townsend's system took the signal from the playback and recording heads and delayed them slightly, producing two sound images from a single original signal. By altering the speed and frequencies, he could also create other effects, which the Beatles used throughout the recording of Revolver.
Producer George Martin described Ken Townsend as one of the studio's "backroom boys." Townsend rarely worked directly with the band, instead working as a maintenance engineer who helped develop studio inventions the Beatles were first to use.