What is "archimago"

Archimago is a sorcerer in The Faerie Queene by Edmund Spenser. His name means "Arch-Image". In the narrative, he is continually engaged in deceitful magics, as when he makes a false Una to tempt the Red-Cross Knight into lust, and when this fails, conjures another image, of a squire, to deceive the knight into believing that Una was false to him.