History of Mastering
The history of mastering at first was not something that was done by one individual. Recording engineers before 1925 used primitive tools such as a stylus that was connected to a diaphragm.
It's source of power before electricity came about in the 1930's was a big acoustical type of horn with a turntable platter that spun by a coiling action by springs. When electricity began to be used for record reproduction, a microphone that was powerful enough was used to guide the cutting stylus through an amplifier. This is how records were pressed originally but not actually pressed but produced. The record pressing technology used today did not come til later.
Enter the dubbing or transfer engineer. This came some time after the second world war. It started the trend where a second engineer was need to cut master discs from session tape. That's right, tape recorders & micro-groove long play discs were introduced to the music industry by this time.
However, engineers in this position were not allowed to have any artistic input on the work like today. They were hardly or never even praised with thanks for their work, but were grateful that their expertise was in demand & very necessary to guarantee that the sound reproduction was an exact copy as the original source.
Afterall there was no way to make any adjustments or corrections afterwards. The resulting sound quality was the responsibility of the people who made the tape for dubbing purposes.