Beltrán Ruiz led one of the busiest Mexican dance orchestras of the 1950s and wrote music for films starring Pedro Infante, Tin Tan and Cantinflas. He is credited as co-composer of “¿Quién será?” and, after buying Demetrio’s rights, often as its sole author. He is also widely named as its first recording artist, on the strength of an uncited claim that his orchestra cut an instrumental cha-cha-chá version in 1953 — but SecondHandSongs dates that performance to 1959 and no 1953 pressing of it has been documented, so this page does not present him as the original recorder.