E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
In Spensers Faëric Queene (ii. 1). He assumes the guise of the Red Cross Knight, and deceives Una; but Sansloy sets upon him, and reveals his true character. When the Red Cross Knight is about to be married to Una, he presents himself before the King of Eden, and tells him that the Knight is betrothed to Duessa. The falsehood being exposed, Archimago is cast into a vile dungeon (book i.). In book ii. the arch-hypocrite is loosed again for a season, and employs Braggadocchio to attack the Red Cross Knight. These allegories are pretty obvious: thus the first incident means that Truth (Una), when Piety (the Red Cross Knight) is absent, is in danger of being led astray by Hypocrisy; but any Infidel (Sansloy) can lay bare religious hypocrisy.
Such whenas Archimago them did view
He weened well to worke some uncouth wyle.
Spenser: Faërie Queene, ii. 1, st. 8.
Sometimes Spenser employs the shortened form Archimage.