Dĭoclētĭānus (noun M) : C. Aurelius Valerius * A Roman emperor from 284-305 A. D., Aurel. Vict. Caes. 38; id. Epit. 39; Eutrop. 9, 13 sq.; before his accession to the throne named Diocles,Aur. Vict. Ep. 39.
Charlton T. Lewis, Charles Short, A Latin Dictionary
PIR
Male Personal name Confirmed occurences in the Roman Empire:
Imp. Caesar C. Aurelius Valerius Diocletianus Aug. (Masc, senator), ref: PIR A 1627 | PIR ID3284
Licinius Diocletianus (Masc), ref: PIR L 0194 | PIR ID8324