Irenaeus (A.D. 180), a student of Polycarp (who was a disciple of the apostle John), wrote that the apocalyptic vision “was seen not very long ago, almost in our own generation, at the close of the reign of Domitian” (Against Heresies 30). The testimony of Irenaeus, not far removed from the apostolic age, is first rate. He places the book near the end of Domitian’s reign, and that ruler died in A.D. 96. Irenaeus seems to be unaware of any other view for the date of the book of Revelation.
Clement of Alexandria
Clement of Alexandria (A.D. 155-215) says that John returned from the isle of Patmos “after the tyrant was dead” (Who Is the Rich Man? 42), and Eusebius, known as the “Father of Church History,” identifies the “tyrant” as Domitian (Ecclesiastical History III.23).
Eastern Orthodox patristic scholar Fr John Behr discusses Irenaeus's words in his book, John the Theologian and his Paschal Gospel. He argues that the subject of the verb "was seen" is John, so that it should be translated "he was seen," not "it was seen."
Clement of Alexandria does not name the tyrant. Eusebius is the first writer to place the exile late in Domitian's reign, so it's hardly surprising he identified the tyrant with Domitian.