The Two Witnesses represent a literary term within DEXTER. In preparation for the End of Days, Two Witnesses enact signs from the Book of Revelation to warn the people while bringing about the End of the Old World. The Witnesses are represented by Travis Marshall and the late Professor James Gellar, whom were meant to display these signs. Professor Gellar did not believe in being one of the witnesses and considered Travis delusional, he was stabbed shortly thereafter by the Sword of John the Revelator which killed him instantly. Travis blocked out this memory after hiding the body and envisioned Professor Gellar once more as an illusion, this time cooperative with their cause.
As one of the witnesses, Travis enacts what are referred to as the Doomsday Tableaus where a human sacrifice is required for each picturesque crime scene. According to notes taken by the original Professor Gellar, creating these events will trigger the End of Days and bring about the New World. In addition, another literary figure is meant to oppose them known as The False Prophet (represented by Dexter Morgan) and has thus far lead to a difficult conflict.
According to the Book of Revelation, both of the witnesses are struck down by The Beast before being resurrected as a display of God's power. If the series follows this translation, then Travis will likely end up dying.