Final answer:
John Hammond was the producer who helped launch Billie Holiday's early career. He was essential in exposing her talent to broader audiences. Additionally, Alan Freed is recognized for popularizing rock and roll.
Step-by-step explanation:
The producer who aided Billie Holiday's early career was John Hammond. John Hammond was a prominent American record producer, civil rights activist, and music critic who discovered and signed some of the greatest names in jazz, blues, and folk music. His work with Billie Holiday in the early stages of her career was instrumental in bringing her talent to a wider audience.
In relation to another aspect of music history, the disc jockey credited with popularizing rock and roll was Alan Freed. Freed was known for promoting African-American music styles for a wider audience in the 1950s and was among the first to play rock and roll music for a mainstream, multi-racial audience. His influence played a substantial role in the development and dissemination of rock and roll music.