Díaz was born in
San Juan, Puerto Rico, the capital of the island, but lived and was raised in the town of
Cataño. He attended Robinson Elementary School where, at the age of 8, he started to participate in the school's activities as a singer. In his first school play, when he was 10 years old, he sang the song "
Old Black Joe", which became his favorite. After finishing his primary education, Díaz attended the
University of Puerto Rico High School in
Río Piedras. While in high school, he took singing classes and participated in various presentations around the island. Díaz joined the choir of the
University of Puerto Rico, under the direction of
Augusto Rodríguez, where he sang solo. His operatic debut was in 1957 as Ben in
Gian Carlo Menotti's ''
The Telephone, or L'Amour à trois''. It wasn't long before Díaz enrolled in
New England Conservatory in
Massachusetts. One of his professors was
Boris Goldovsky, who would be very influential in his career. Díaz made his professional debut as an opera singer at the Opera Theater of New England. In 1960, Goldovsky asked Díaz to join his opera company on a 20-state tour. After the tour, he entered and participated in a competition celebrated at the
Metropolitan Opera House, winning third place in the
New England region. Díaz moved to
New York upon finishing his studies at the conservatory. Goldovsky recommended that he be represented by Hans J. Hoffman, a talent agent. Soon, Díaz was singing alongside other artists at the
American Opera Society. He also sang with the Rochester Philharmonic Orchestra and the
Boston Symphony Orchestra. ==Metropolitan Opera==