Final answer:
Eleanor Roosevelt was the prominent figure who hired a black female vocalist to perform at a white nightclub, challenging racial barriers and changing perceptions about African American female vocalists.
Step-by-step explanation:
The significant female vocalist who was the first black vocalist to be hired by a white bandleader and who came to prominence while performing at the New York nightclub called Cafe Society was Eleanor Roosevelt. Roosevelt was instrumental in changing perceptions about female vocalists, particularly those who were African American, during a time of significant racial segregation and discrimination. Her actions in inviting African American guests to the White House and eventually arranging for Marian Anderson to sing at the Lincoln Memorial showcased her support for civil rights and her role in elevating the status of black artists.