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Bob Gaudio
Robert John Gaudio (born November 17, 1942) is an American singer, songwriter, musician, and record producer, and the keyboardist and backing vocalist of the pop/rock band the Four Seasons. Gaudio wrote or co-wrote and produced the vast majority of the band's music, including hits like "Sherry" and "December, 1963 (Oh, What a Night)". Though he no longer performs with the group, Gaudio and lead singer Frankie Valli remain co-owners of the Four Seasons brand.
Source: Wikipedia