Francesco Stephen Castelluccio (born May 3, 1934), better known by his stage name Frankie Valli, is an American singer, known as the frontman of the Four Seasons beginning in 1960. He is known for his unusually powerful lead falsetto voice.

Valli scored 29 top 40 hits with the Four Seasons, one top 40 hit under the Four Seasons alias the Wonder Who?, and nine top 40 hits as a solo artist. As a member of the Four Seasons, Valli's number-one hits include "Sherry" (1962), "Big Girls Don't Cry" (1962), "Walk Like a Man" (1963), "Rag Doll" (1964) and "December, 1963 (Oh, What a Night)" (1975). Valli's recording of the song "Can't Take My Eyes Off You" reached number two in 1967. As a solo artist, Valli scored number-one hits with the songs "My Eyes Adored You" (1974) and "Grease" (1978).

Valli, Tommy DeVito, Nick Massi and Bob Gaudio – the original members of the Four Seasons – were inducted into the Rock and Roll Hall of Fame in 1990 and the Vocal Group Hall of Fame in 1999.