To Mega Therion or Το Μεγα Θηριον is Greek for "The Great Beast" and is a reference to the Book of Revelation:

Revelation 13:1 And I stood upon the sand of the sea, and saw a beast [θηριον, therion] rise up out of the sea, having seven heads and ten horns, and upon his horns ten crowns, and upon his heads the name of blasphemy. 2 And the beast which I saw was like unto a leopard, and his feet were as the feet of a bear, and his mouth as the mouth of a lion: and the dragon gave him his power, and his seat, and great authority.

The name does not actually occur in the form "To Mega Therion" in the Greek text of the Book of Relevation, but the title was taken by the English occultist Aleister Crowley, who believed that he was destined to destroy Christianity.

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