He was associated by his father in ruling Gaeta in early 877 or before, as shown by a letter of Pope John VIII dated 9 Apr 877 addressed to "Decibili et Iohanni hypatis" thanking them for attacking the Saracens. The testament of "Docibilis ypatus civitatis istius Gaietane", dated 906, names his wife (and her father) and his children (in order) "Bona, Maria, Euphemia, Jean, Léon, Anatole, Megalu".
He succeeded his father as Lord [prefect/hypatos] of Gaeta. He was granted the Byzantine title patrikios in 914 by the Byzantine strategos in Campania in an attempt to get the support of Gaeta in fighting the Arabs. He participated in the expedition which removed the Arab settlement from the mouth of the River Garigliano in 915, for which he was rewarded with a confirmation of the transfer of Fondi and Traetto by Pope John X. A charter dated Jun 933 records a donation with the consent of "domni Iohannis imperiali patricii et domni Docibili seu domni Iohannis…duces et ypati".
The name of Ioannes´s wife is not known. 1
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