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.

Born in the Bronx, New York, Gaudio was raised in Bergenfield, New Jersey, where he attended Bergenfield High School. His mother worked for the publishing house Prentice Hall and his father in a paper factory. He showed an interest in music and studied piano with Sal Mosca.

He grew up in more comfortable middle-class surroundings than the other members of the Four Seasons, which caused some tension and differences early on. He was a cerebral person, interested in reading and learning. He stayed out of trouble and had a mild manner, which proved useful during negotiations throughout his career.

He rose to musical fame at the age of 15 as a member of The Royal Teens, for whom he co-wrote the hit "Short Shorts". In 1958, while he and the group were promoting the single, they met Frankie Valli and his group the Four Lovers as they prepared to perform on a local television program. Wearying of touring, Gaudio left the Royal Teens soon afterward.

One year after he ceased touring, Gaudio joined the Four Lovers. While commercial success was elusive, the group was kept busy with session work (with Bob Crewe as the producer), and a string of performances at night clubs and lounges.

In 1960, after a failed audition at a bowling establishment in Union Township, called the "4 Seasons", songwriter/pianist Gaudio shook hands with lead singer Valli and formed the Four Seasons Partnership, and Gaudio, Valli, Tommy DeVito, and Nick Massi became The Four Seasons.

Gaudio wrote the Seasons' first No. 1 hit, "Sherry", 15 minutes before a group rehearsal in 1962. With producer Bob Crewe often assisting with lyrics, Gaudio wrote a string of subsequent hits for the Seasons, including "Big Girls Don't Cry", "Walk Like a Man", "Dawn (Go Away)", "Ronnie", "Rag Doll", "Save It for Me", "Big Man in Town", "Bye Bye Baby", "Girl Come Running", "Beggin'", and "Can't Take My Eyes Off You" (the first big success under Valli's name as a solo performer). Crewe/Gaudio compositions also became major hits for other artists, including the Tremeloes ("Silence Is Golden", originally the B-side of the Four Seasons' "Rag Doll"), The Osmonds ("The Proud One", originally recorded as a Valli solo single) and the Walker Brothers ("The Sun Ain't Gonna Shine Anymore", another Valli single).

After the Beatles' Sgt. Pepper's Lonely Hearts Club Band album was released in June 1967, Gaudio saw the pop music market changing, and sought to position the Four Seasons into the trend of socially conscious music. One evening he went to the Bitter End in Greenwich Village and saw Jake Holmes performing. Gaudio was taken with Holmes' song "Genuine Imitation Life" and decided to base a Four Seasons album upon it. With Holmes as his new lyricist, The Genuine Imitation Life Gazette album was released in January 1969. The album was a commercial failure and symbolized the end of the Four Seasons' first period of success. The appreciation of The Genuine Imitation Life Gazette has grown over the years, and it was re-released on CD (minus the newspaper cover) in the 1990s by Rhino in the U.S. and Ace in the UK. Gaudio and Holmes also wrote and produced Frank Sinatra's 1969 album Watertown.