His father associated him in the government of Gaeta in early 914, as shown by the charter dated Jun 914 which records the consent of "domni Iohannis et domni Docibili…ypati". 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".
He succeeded his father as Lord [prefect/hypatos] of Gaeta. He was the first of his family recorded (for the first time in 933) as having used the title dux.
The testament of Docibilis [II], dated May 954, names "Marino duci et…Gregorio et…Leone filiis meis". 1
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