Final answer:
The musical guest that broke every single-night rating record and increased popularity in 1956 was Elvis Presley.
Step-by-step explanation:
The musical guest that rocketed the ratings of a show in 1956 to break every single-night rating record was Elvis Presley. His appearance on The Milton Berle Show triggered huge controversy and drove teenage listeners wild with his sultry looks, swinging hips, and dynamic vocal style. Elvis Presley's music and performances played a significant role in popularizing rock and roll during that time.