One of the more prolific and/or legendary music producers of the 1960s, 70s, and beyond was Phil Spector. Spector worked with female vocal groups like The Crystals and The Ronettes, before producing The Beatles' Let It Be and several George Harrison and John Lennon solo works. He even produced one album for The Ramones. Then he became a convicted murderer and went to prison, but that is strictly besides the point.
What made Spector so legendary wasn't just the fact that he worked with awesome acts that happened to churn out lots of hits. Spector was also an innovator of one of the more important musical techniques of the 20th century. There is heavy debate over whether Spector's "Wall of Sound" did more to help or to hurt the music industry, but there is no denying its impact.
The wall of sound was generally carried out on monophonic recordings, despite the traction that stereophonic recordings were gaining at the time. Spector disliked stereo recordings, saying that they took the power of the recording away from the producer and gave it to the listener instead. Were it not for the recording techniques used, Spector's songs would have had a much more flat, dull sound, seeing as they were mono recordings. Instead, the wall of sound created a rich sound with much more depth than the usual mono records.
For a more in-depth look at how the wall of sound worked, I recommend checking out this video:
Spector's work on The Beatles' Let it Be was extensive. The most controversial work he did was on "The Long and Winding Road," the production of which angered Paul McCartney so much that he cited it as one of the reasons for dissolving the band.
Tracks like "Be My Baby" and "Sleigh Ride" by The Ronettes are widely recognized as vivid examples of the technique. But the wall of sound was used in many places at the time and continues to be used to this day. During the 60s, the "Wall of Sound" technique was utilized by Brian Wilson of The Beach Boys on Pet Sounds and Smile as well as other works. Producer Johnny Franz also used a similar technique on his production for Dusty Springfield and The Walker Brothers.
In the 70s and 80s, techniques similar to the Wall of Sound were used by Queen, ABBA, and Bruce Springsteen.
These days, Wall of Sound techniques have developed into several musical genres, in addition to the throwback sound trend utilized by groups like She & Him. Shoegazing, Noise Pop, and Dream Pop all find their roots in the Wall of Sound in different ways. Dream Pop finds roots directly in George Harrison's All Things Must Pass, a Spector work.
Wall of Sound is definitely a technique that has had a great deal of influence over music in the last fifty to sixty years. The musical world would be very different without it.