Nero killed himself in 68 and the eastern provinces did not entirely believe it. At least three men claimed to be him in the following decades and attracted support, and the expectation that he would return, from beyond the Euphrates and at the head of an army, appears in the Sibylline Oracles and elsewhere. That is the background to the most discussed identification in the book of Revelation.
The number of the beast, six hundred and sixty six, has been read as a cipher for his name since the nineteenth century, on the following ground. Written in Hebrew letters, which carry numerical values, the Greek form Neron Caesar totals 666. Some manuscripts of Revelation give the number as 616 instead, and the Latin form Nero Caesar, without the final letter of Neron, totals exactly 616 by the same method. A cipher that explains both the number and its variant is a strong argument, and it is the reason this reading is widely held. It remains an inference. The text does not name him, the practice of encoding names in numbers was common enough to generate coincidences, and other candidates have been proposed. The atlas records it as the best supported reading and not as a certainty.
What the identification does explain, if it is right, is the tone of the book. A community writing under an emperor who has already killed its members, in a province where he is expected to come back at the head of an army, has a concrete reason to describe a beast that had a mortal wound and recovered. The atlas notes that the reading gains its force from the historical setting rather than from the arithmetic alone, and that the arithmetic on its own would not persuade anyone.