Castel was raised in Venezuela by multilingual parents and a German nanny and attended a French school in Caracas.
On the concert stage, Castel often included Jewish music in his programs, and he served as a cantor at synagogues; he wrote a Ladino songbook.
Castel was born in Lisbon, Portugal, the "scion of a multigenerational dynasty of Sephardic rabbis" with roots in 15th century Castile.
[1][2] In 1958, he became the first winner of the "Joy in Singing" award, which launched his career with a recital at The Town Hall in New York City.
The New York Times commented: "Reviewers over the years praised Mr. Castel’s rich dramatic characterizations, his sensitive musicianship and, not surprisingly, his impeccable diction.
"[1] A polyglot, Castel spoke Portuguese, Ladino, German, French, Spanish, Italian and English with native or near-native fluency.
He was an internationally known language and diction coach, writing the book A Singer’s Manual of Spanish Lyric Diction and translating an extensive annotated series of librettos of French, German and Italian operas, adding the pronunciation of every word in the operas' original languages using the International Phonetic Alphabet.
[7] Among Castel's recordings are Manon (with Beverly Sills, 1970) and The Tales of Hoffmann (with Sills and Norman Treigle, 1972), both conducted by Julius Rudel, and a live performance from the Metropolitan Opera of Ariadne auf Naxos (1988, with Jessye Norman, Tatiana Troyanos, and Kathleen Battle, conducted by James Levine; issued on DVD).