Robert John Gaudio (born November 17, 1942) is an American songwriter, singer, musician, and record producer, and the keyboardist and backing vocalist of the pop/rock band the Four Seasons. Gaudio wrote or co-wrote the vast majority of the band's music, including hits like "Sherry" and "December, 1963 (Oh, What a Night)", as well as "Can't Take My Eyes Off You" for Valli. Though he no longer performs with the group, Gaudio and lead singer Frankie Valli remain co-owners of the Four Seasons brand.

https://en.m.wikipedia.org/wiki/Bob_Gaudio