Descartes' First Meditation

A belief is practically certain ('morally certain' in Cartesian terms) for a person, S, at a time, t, just in case it is justified well enough for the ordinary affairs of life for S at t.
 
A belief is metaphysically certain for a person, S, at a time, t, just in case there is not even the "least ground of suspicion against it" at t.
 
Epistemic Purification: If everything that a person, S, believes at a time, t, is a metaphysical certainty for him at t, then S is epistemically purified at t.
 
Descartes' Assumption: It is within our power to stop believing things that we now believe.
 
Descartes' Epistemic Principle: Once in his or her life, a person who seeks maximal epistemic purification must suspend judgment on everything that is less than metaphysically certain.

 
The Dream Argument
 
1. There is no criterion by which I can determine that I am not dreaming.
2. If (1), then everything that I formerly believed is less than metaphysically certain.
3. If everything that I formerly believed is less than metaphysically certain, then I must refrain from believing everything I formerly believed in my quest for epistemic purity.
4. Therefore, I must refrain from believing everything I formerly believed in my quest for epistemic purity. [1,2,3 MMP]

 
The Deceptive God Argument
 
1. Either I was created by God or I was created by something less powerful than God.
2. If I was created by God, then I was created by something powerful enough to make me go wrong in what seems most certain.
3. If I was created by something less powerful than God, then it's possible that I have defective epistemic faculties.
4. Therefore, either I was created by something powerful enough to make me go wrong in what seems most certain or it's possible that I have defective epistemic faculties. [1,2,3 CD]
5. If I was created by something powerful enough to make me go wrong in what seems most certain, then everything that I formerly believed is less than metaphysically certain.
6. If it's possible that I have defective epistemic faculties, then everything that I formerly believed is less than metaphysically certain.
7. Therefore, everything that I formerly believed is less than metaphysically certain. [4,5,6 SC]
8. If everything that I formerly believed is less than metaphysically certain, then I must refrain from believing everything I formerly believed in my quest for epistemic purity.
9. Therefore, I must refrain from believing everything I formerly believed in my quest for epistemic purity. [7,8 MP]

Can you explain the role of the "Evil Demon" hypothesis in the Meditations.