Roger Chillingworth is the antagonist in that he's the main impediment to Hester and Dimmesdale's happiness. This is because he represents the stern moral values of Puritanism, with its strict moral code and firm, unwavering belief in the fundamental depravity of each human being.
Instead of using his medical training—not to mention his religious values—to help a clearly troubled soul, Chillingworth abuses his authority to torture Dimmesdale psychologically, actually becoming more physically repulsive the more he torments his patient. It's no exaggeration to say that Chillingworth lives for destroying Dimmesdale and Dimmesdale's plans for happiness. So determined is he to carry out this diabolical scheme that he buys a ticket for the same ship as Dimmesdale and Hester, hoping to follow them to Europe.
It's instructive that once Dimmesdale has publicly confessed of his sins, Chillingworth effectively gives up the ghost. Not long after Dimmesdale's death, Chillingworth follows him to the...
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