America's first major prima ballerina worked for which ballet company? 
Nicholas Magallanes:  Along with Jerome Robbins, Francisco Moncion and Maria Tallchief, Magallanes was among the core group of dancers with which George Balanchine and Lincoln Kirstein formed the New York City Ballet (formerly "Ballet Society") in 1948. Maria Tallchief:  She was considered America's first major prima ballerina, and was the first Native American to hold the rank.
New York City Ballet