It was William Blake who observed that Milton belonged to the Devil's party without knowing it. The remark implies that Milton unconsciously glorified Satan, especially in Book-I of Paradise Lost. This point of view is typical of the Romantic spirit, and it makes Satan the real hero of Paradise Lost. The Romantics admired indomitable courage and love of freedom, both of which Satan shows in plenty of Book-I of Paradise Lost. However, one cannot admire these qualities as good in themselves, ignoring the moral values connected with them in the context of the poem.
Satan certainly possesses heroic qualities in Paradise Lost, but, if Milton glorified him, it is done consciously. But knowingly or unknowingly, Milton is never on the side of the Devil. Satan was required to be made of heroic dimensions to make him a fitting adversary of God and to impress on the reader the dangerous potential of evil. Furthermore, if Satan had been of less than ordinary stature, the deception of the Mother of Mankind would lose its effectiveness. Above all, Milton was writing a special kind of epic - an epic of cosmic proportions which required its characters to be impressive.
Satan cannot, however, be regarded as the "hero" of the poem merely because he is cast in the heroic mould. The courage, the determination, the philosophical statements, the love of freedom, all these qualities lose their value when the intention behind them becomes clear - and it is clear not merely in Milton's commentaries but in Satan's very speeches. One should not be deceived by the dazzling flourishes of Satan's rhetoric. Milton's presentation of Satan is in no way at variance with his commentary. Satan comes out in all his vain egotism, falsehood and evil. His courage and indomitable will are directed towards evil -"our labour must be to pervert that end and out of good still to find means of evil." Satan is the negation of good. He is the perversion of an angelic nature. While this perversion is increasingly evident in the later Books of Paradise Lost, it is also very much there in Book-I. He intends the war against God to be conducted by guile, anticipating the sly and sneaky manner in which he enters the Garden of Eden to harm two beings who have done him no harm.
The grandeur that Milton bestows on Satan is the fulfillment of an artistic requirement. But a villain is a villain however powerful he is portrayed. Even from Book-I of Paradise Lost Satan appears as the father of lies, an arch-fiend, an apostate angel, an archangel ruined. He would have been a tragic hero if he had opposed forces of evil, but ironically he is himself the author of evil. The great qualities of Satan are made futile because of his inner corruption. As B.A. Wright points out, Satan is the enemy of God and man. He must be seen as a towering genius, but we cannot forget that his genius is Satanic. "All his virtue are in fact corrupted by his situation and by the uses to which he puts his power." When we read Satan's speeches and understand their implication, we cannot endorse the opinion that Milton belonged to the Devil's party, knowingly or unknowingly. We do not feel that the poet's commentaries are at variance with the presentation of Satan. We realize that if Milton has "glorified" Satan it is to make all the more poignant the idea that mere appearance is not enough and that one should not be deceived by the dazzle in which evil clothes itself.