Ethos, logos, and pathos are the three pillars of classical persuasion. Ethos is persuasion based on character or credibility. Logos is persuasion based on logic: facts and statistics. Pathos is emotional persuasion: we are convinced to pursue a course of action because we have been made frightened, hopeful or been played on successfully by some other emotion.
From the start of Book I, as he summarizes Satan's and his minion's fall into the pit of hell, Milton surrounds Satan with a negative ethos: he is described in terms that show him to be an evil character: he is a "serpent," one who stirs up "Envy and Revenge," deceitful, proud, "ambitious," "impious" and the enemy of God. He is:
Th' infernal Serpent; he it was, whose guile
Stird up with Envy and Revenge, deceiv'd
The Mother of Mankind, what time his Pride
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