John I (died 933 or 934) was the second hypatus of Gaeta of his dynasty, a son of Dociblis I and Matrona, and perhaps the greatest of medieval Gaetan rulers.
He began his rule as an associate of his father from either 867, right after his father's violent takeover, or 877, when he is first mentioned as co-regent. In that year he received the honorific patrikios from Byzantine Emperor Constantine VII. His father disappears from the annals in 906, but he is only confirmed dead in 914. Nonetheless, the intervening period was John's. He recognised his brother Anatolio as duke of Terracina and sold the castle of Dragoncello to his other brothers. He began to reverse the policy of his father of alliance with the Saracens and war with his Lombard and Greek neighbours. He married his daughters off strategically: Gemma to the Sorrentine prefect Marinus, Maru to the Salernitan nobleman Guaifer, and Matrona to Campolo, of an important Gaetan family. Probably from the earliest, in 906, John associated his own son Docibilis in a co-regency, certainly by 914.
Together, father and son joined the Byzantine strategos Nicholas Picingli's army marching with its Lombard allies to meet the papal and Spoletan forces. All together, the Christian league attacked the Moslems of the Garigliano and, in the subsequent battle, the Gaetan hypati distinguished themselves in victory. The Gaetan territory was extended to the Garigliano River. John continued construction on the palace his father had begun and he associated his grandson, John II, with him in 933. He died within the year and left three other sons (Leo, Constantine, and Peter), but Docibilis, who had taken the ducal title in 930, inherited alone and did not divide the realm. Thus, John is the last ruler of Gaeta who was not a duke.