The Number of the Beast is described in the Book of Revelation 13:17–18. In the Textus Receptus (derived from Byzantine text-type manuscripts), it is written:
17 και ινα μη τις δυνηται αγορασαι η πωλησαι ει μη ο εχων το χαραγμα η το ονομα του θηριου η τον αριθμον του ονοματος αυτου 18 ωδε η σοφια εστιν ο εχων τον νουν ψηφισατω τον αριθμον του θηριου αριθμος γαρ ανθρωπου εστιν και ο αριθμος αυτου χξς.
The number is the final 3 letters or words (transliterated: χξς’ or ἑξακόσιοι ἑξήκοντα ἕξ), it is "six hundred sixty-six."
The King James Version of the Bible translates it as:
And that no man might buy or sell, save he that had the mark, or the name of the beast, or the number of his name. Here is wisdom. Let him that hath understanding count the number of the beast: for it is the number of a man; and his number is Six hundred threescore and six.
In the Old Testament, both 1 Kings 10:14 and 2 Chronicles 9:13 state that Solomon collected "six hundred threescore and six" talents of gold each year. John's reference to "wisdom" and "understanding" might also point toward Proverbs 1 and 2, where understanding, discernment, wisdom and insight are explained and advised by King Solomon. In the Greek manuscripts, the number is rendered in Greek numerical form as χξϛʹ, or sometimes literally as ἑξακόσιοι ἑξήκοντα ἕξ, hexakósioi hexēkonta héx, "six hundred and sixty-six".
There are several interpretations-translations for the meaning of the phrase "Let him that hath understanding count the number of the beast" where the peculiar Greek word ψηφισάτω (psefisato) is used. Possible translations include not only "to count", "to reckon" but also "to vote" or "to decide".
Although Irenaeus (2nd century AD) affirmed the number to be 666 and reported several scribal errors of the number, there is still doubt by a minority of theologians about the original reading.
Many scholars who are of the Preterism way of thinking (those that are concerned with Revelation events that have happened) have said that the Beast of 666 has already been & gone. So let's see who the main contenders were...
NERO
Some contend that the number 666 is a code for the Roman Emperor Nero.Charagma is well attested to have been an imperial seal of the Roman Empire used on official documents during the 1st and 2nd centuries. In the reign of Emperor Decius (249–251 AD), those who did not possess the certificate of sacrifice (libellus) to Caesar could not pursue trades, a prohibition that conceivably goes back to Nero, reminding us of Revelation 13:17. However, others believe the Book of Revelation was written after Nero committed suicide in AD 68.
The Catholic Encyclopaedia has noted that Revelation was "written during the latter part of the reign of the Roman Emperor Domitian, probably in A.D. 95 or 96". Additional Protestant scholars are in agreement. Because some believe Revelation 13 speaks of a future prophetic event, "All who dwell on the earth will worship him, whose names have not been written in the Book of Life of the Lamb slain from the foundation of the world." (Revelation 13:8 NKJV), some have argued that the interpretation of Nero meeting the fulfilment is an impossibility if Revelation was written around 30 years after the death of Nero.
However, rumours circulated that Nero had not really died and would return to power. It has also been suggested that the numerical reference to Nero was a code to imply but not directly point out emperor Domitian, whose style of rulership resembled that of Nero and who put the people of Asia (Lydia), whom the Book of Revelation was primarily addressed to at the time, under heavy taxation.
The Greek spelling, "Nerōn Kaisar", transliterates into Aramaic as "נרון קסר", nrwn qsr. The Aramaic spelling is attested in a scroll from Murabba'at dated to "the second year of emperor Nero."
This then leads us onto one section that I have found seem to think is definitely the Beast mentioned in Revelation...
THE PAPACY
Some Protestant Bible commentators and some Protestant Reformers have equated the "beast" of Revelation chapter 13 with the Papacy. To this end, the letters of a title of the Pope, Vicarius Filii Dei (Vicar of The Son of God), are summed to total 666 in Roman numerals.
The earliest extant record of a Protestant writer on this subject is Andreas Helwig in 1612 in his work Antichristus Romanus. The title was contained in the Donation of Constantine, by which large privileges and rich possessions were conferred on the pope and the Roman Church.
Seventh Day Adventists have interpreted the number of the beast, 666, as corresponding to the title Vicarius Filii Dei of the Pope. The number 666 is calculated by using gematria.
In 1866, Uriah Smith was the first to propose the interpretation to the Seventh-day Adventist Church. In The United States in the Light of Prophecy he wrote
The pope wears upon his pontifical crown in jeweled letters, this title: "Vicarius Filii Dei," "Viceregent of the Son of God;" the numerical value of which title is just six hundred and sixty-six The most plausible supposition we have ever seen on this point is that here we find the number in question. It is the number of the beast, the papacy; it is the number of his name, for he adopts it as his distinctive title; it is the number of a man, for he who bears it is the "man of sin."
Prominent Adventist scholar J. N. Andrews also adopted this view. Uriah Smith maintained his interpretation in the various editions of Thoughts on Daniel and the Revelation, which was influential in the church.
Various documents from the Vatican contain wording such as "Adorandi Dei Filii Vicarius et Procurator quibus numen æternum summam Ecclesiæ sanctæ dedit" which as translated is "As the Vicar and Caretaker of the worshipful Son of God, to whom the eternal divine will has given the highest rank of the Holy Church".
Samuele Bacchiocchi a Bible scholar, and only Adventist to be awarded a gold medal by Pope Paul VI for the distinction of summa cum laude (Latin for "with highest praise").[42] has documented the pope using such a title.
MUHAMMAD
Some researchers have reportedly found the number of the Beast in the Greek word Maometis. In Quia Maior, the encyclical calling for the Fifth Crusade, Pope Innocent III identifies Muhammad with the beast of Revelation (however later popes do not).
A leading exponent of the Maometis interpretation was Charles Walmesley, the Roman Catholic bishop of Rama. He observed that the name Muhammad was spelled Maometis or Moametis by Euthymius Zygabenus and the Greek historians Zonaras and Cedrenus.Other proponents include Charles Montagu, Gilbert Genebrard, Francois Feuardent, and Rene Massuet. Maometis in Greek gematria totals 666.
CONCLUSION
I personally don't think that Muhammad was the Beast prophesied, not because I'm afraid of the consequences if I say I think he was, just that my instincts (which are nearly always correct) tell me that he just isn't. And if he were, why would the Beast accept that Jesus was a Messiah for the Jewish people & a Prophet? It just doesn't make sense to me.
My thoughts of Nero is that it could well have been him as the Bible WAS written for those to understand during that time period, but a lot of what was written about the end times haven't actually come to pass yet.
I think that the Beast of the Revelation & other Religions has not appeared yet. Do I know who it is? I have my opinions that I may let you in on......in time.