Moreno was born Rosa Dolores Alverio in Humacao, a small town near the Puerto Rican rain forest. At age 5, she moved with her mother to New York where the precocious child soon began dance lessons. She made her Broadway debut at just 13 in Skydrift, starring Eli Wallach. Then, in true Hollywood tradition, a talent scout spotted her and arranged for the teen to meet MGM mogul Louis B. Mayer, who signed her to a film contract.