The speaker of Carol Ann Duffy's "Medusa" does not hold back regarding her anger and fury toward men. Metaphorically, the speaker compares her own situation to that of Medusa being raped by Poseidon while worshiping in Athena's temple (according to one myth). Medusa's torment does not end with her rape; instead, Athena turns her into a gorgon.
The speaker of the poem proves to be complex. Not only does the speaker turn herself into Medusa (figuratively), her suspicion and jealousy has made her foul breathed and tongued. Her husband, she states, should be very worried about her wrath. Essentially, the speaker (although she loves her man) knows he will betray her eventually. She does not care though--she simply becomes hard-hearted.
She realizes that before her suspicion and jealousy reared their ugly heads that she was beautiful. Now, she feels ugly, old, and smelly. The speaker realizes how powerful jealousy and suspicion can be.
The characterization of the speaker is important to the poem because of the way jealousy transforms her. It speaks to the fact that negative things in one's life can eat them alive and change them (both internally and externally). Without this very specific and horrifying image, the speaker's point may not have gotten across to readers. The image that jealousy can change one into Medusa is rather shocking (and honest).