MONO is how most listeners first heard Elvis in the 1950s and 1960s, when it was the predominant audio format. Until 1968, each Elvis album was given a unique MONO and STEREO mix, but Elvis always regarded the MONO mix as primary. This was also true for singles. Up until affordable home STEREO systems in the late 1960s, the record industry always regarded STEREO as secondary, going back to its debut in the late 1950s. MONO singles, EPs and LPs were the standard for retail and radio.
The recorded legacy of Elvis Presley continues to be discovered by new generations that never saw him or heard him perform live. It's hard to appreciate that he started so much of what we take for granted now in popular music. Until 1956, the teenagers of suburban America, and the rest of the world, had to endure ditties by Rosemary Clooney and Perry Como but everything was about to be tossed upside down. On January 28 on a cold night in New York, Elvis took America by storm as he appeared on CBS-TV's Stage Show hosted by Jimmy and Tommy Dorsey. On February 4 for his second appearance he sang a song that literally changed the world of popular music "Heartbreak Hotel". Its unique sound and style literally blew everything before it away while at the same time inducing the blueprint for everything that was to come; by April, it would be #1 on Billboard.
It is no exaggeration to call Little Walter the Jimi Hendrix of the electric harp: he redefined what the instrument was and what it could do, pushing the instrument so far into the future that his music still sounds modern decades after it was recorded. Little Walter wasn't the first musician to amplify the harmonica but he arguably was the first to make the harp sound electric, twisting twitching, vibrant runs out of his instrument; nearly stealing the show from Muddy Waters on his earliest Chess recordings; and so impressing Leonard Chess that he made Muddy keep Walter as his harpist even after Waters broke up his band. Chess also made Walter into his studio's house harpist and started to release Little Walter solo records with the instrumental "Juke" in 1952. "Juke" became a smash hit and turned Little Walter into a star, making him a steady presence on the '50s R&B charts.