Satan, as a character, has been satirized, mocked and made foolish in our modern world. John Milton, however, presents quite a different Satan from the devil-on-your-shoulder image people are used to seeing. In Paradise Lost, Milton draws on the Bible for his source of Satan's character, thereby creating a horrifyingly corrupt Satan. Despite this portrayal, readers often find themselves sympathizing with Satan's cause, and his determination, viewing him as a hero for his cause, as evidenced by his long, brave speeches. Later, however Satan's speeches begin to show signs of regret, making the reader question their initial reaction to him....
Satan's good points first. Then, when Satan's real character begins to emerge, the reader is appalled at the actions of their "hero", causing them to dislike him more than had he originally been a bad character. The reader's distaste for Satan is strengthened by Satan's shift in motives. The conquering of humans, which he originally presented as a rebellion against God and his authoritative rule, later came to be about pure corruption and hate. It's therefore possible to say that if Satan had never given up on his original reasoning, he would still be the hero of Paradise Lost.