Giovannino Zeti was the keeper of the garrison at Monteriggioni and a Florentine exile. He worked directly for the House of Auditore, the rulers of Monteriggioni.

In 1554, after Monteriggioni withstood a series of attacks from Florence, Zeti betrayed the garrison when he was allowed to return to Florence in exchange for the keys to the city. Consequently, Monteriggioni was conquered by Florence, though the Auditore were allowed to remain rulers of the city.