Although the savage who kidnaps and almost rapes Amoret in Book 4 is never named, his associations with unbridled lust make him such a clear embodiment of that sin that some critics just go ahead and call him Lust. As you've probably picked up by now, there are quite a few representations of negative or overly sensual sexuality in this poem, but what makes the savage different is a) his gender (the majority of lustful figures are women) and b) his uncultivated and even uncivilized nature (the majority of lustful figures are also rich, powerful, and live lavishly).
The Savage, instead of embodying the luxurious temptation of lust that was so explicitly part of the Bower of Bliss (see Symbols, Allegories, Images), he embodies its brutal and violent side, not waiting for consent or using seduction. The fact that he practices cannibalism after raping his victims further associates him with crude, sadistic, and ferocious brute force.
The Savage is clearly not a delightful character, but there's is an even ickier, racial element to his representation that bears mentioning. As his name suggests, the Savage is quite clearly based on accounts of aboriginal and native peoples that were just being discovered by Europeans in the Americas while Spenser was writing.
Europeans thought these people lived a "savage" existence since it was different from sixteenth century European ways of life. Soon, widely exaggerated reports of their cannibalistic practices spread throughout Europe and clearly inspired Spenser's character. The idea that these people lacked rationality and an ability to control their "baser" passions—like sexuality—was also a widespread belief about them.