Roger Chillingworth, unlike Hester and Dimmesdale, is a flat character. While he develops from a kind scholar into an obsessed fiend, he is less of a character and more of a symbol doing the devil's bidding. Once he comes to Boston, we see him only in situations that involve his obsession with vengeance, where we learn a great deal about him.
Hawthorne begins building this symbol of evil vengeance with Chillingworth's first appearance (". . . dropping down, as it were, out of the sky, or starting from the nether earth . . .") in the novel by associating him with deformity, wildness (the Indians), and mysterious power. Having just ended over a year of captivity by the Indians, his appearance is hideous, partly because of his strange mixture of "civilized and savage costume."
Even when he is better dressed, however, Chillingworth is far from attractive. He is small, thin, and slightly deformed, with one shoulder higher than the other. Although he "could hardly be termed aged," he has a wrinkled face and appears "well stricken in years." He has, however, a look of calm intelligence, and his eyes, though they have a "strange, penetrating power," are dim and bleared, testifying to long hours of study under lamplight.
The reader feels a bit sorry for Roger Chillingworth during the first scaffold scene when he arrives in Massachusetts Bay Colony and finds his wife suffering public shame for an adulterous act. At that point, however, he has several choices; he chooses revenge. His rude awakening is described a second time in Chapter 9 when Hawthorne calls him "a man, elderly, travel-worn, who, just emerging from the perilous wilderness, beheld the woman, in whom he hoped to find embodied the warmth and cheerfulness of home, set up as a type of sin before the people." What should have been a warm and loving homecoming after being apart from his wife has become terrible.
Chillingworth is not a Puritan. While he was a captive of the Indians for "upward of a year," he did not judge them as heathens and infidels, and, unlike the Puritans, he did not seek to convert them. Instead, as the scholar, he studied their knowledge of herbs and medicines to learn. He has, indeed, spent his life as a lonely scholar, cutting himself off when necessary in the quest for knowledge from the world of other men. This study of herbs and medicines later links his work to the "black medicine" and helps him keep his victim alive.
Hawthorne further develops this "other world" involvement — whether fate or predetermined by some higher power — when he describes the physician's appearance as being just in time to "help" Dimmesdale. The Puritans believed that the hand of God, or Providence, was in every event. So Hawthorne skewers their belief in mentioning Chillingworth's arrival when he states, "Individuals of wiser faith, indeed, who knew that Heaven promotes its purposes without aiming at the stage-effect of what is called miraculous interposition, were inclined to see a providential hand in Roger Chillingworth's opportune arrival."
When Chillingworth arrives in the colony and learns of Hester's situation, he leaves her alone nearly seven years as he single-mindedly pursues Dimmesdale. He does, however, see his role in her downfall. Because he married her when she was young and beautiful and then shut himself away with his books, he realizes that their marriage did not follow "the laws of nature." He could not believe she, who was so beautiful, could marry a man "misshapen since my birth hour." He deluded himself that his intellectual gifts dazzled her and she forgot his deformity. He now realizes that from the moment they met, the scarlet letter would be at the end of their path.
His love of learning and intellectual pursuit attracts Dimmesdale. In the New World, men of learning were rare. Hawthorne says, "there was a fascination for the minister in the company of the man of science, in whom he recognized an intellectual cultivation of no moderate depth or scope; together with a range and freedom of ideas that he would have vainly looked for among the members of his own profession." This love of wisdom is what will draw the two men together, thus facilitating Chillingworth's plans.
In Chillingworth, Hawthorne has created the "man of science," a man of pure intellect and reason with no concern for feelings. Notice the "chilliness" of his name. In Chapter 9, Hawthorne describes the scarcity of Chillingworth's scientific peers in the New World: "Skillful men, of the medical and chirurgical profession, were of rare occurrence in the colony." These men of science have lost the spiritual view of human beings because they are so wrapped up in the scientific intricacies of the human body. As a paragon of this group, Chillingworth lives in a world of scholarly pursuits and learning. Even when he was married to Hester, a beautiful, young woman, he shut himself off from her and single-mindedly pursued his scholarly studies.
Once Chillingworth decides to pursue Hester's lover and enact revenge, he pursues this purpose with the techniques and motives of a scientist. Moving in with Dimmesdale he pokes and prods. His hypothesis is that corruption of the body leads to corruption of the soul. "Wherever there is a heart and an intellect, the diseases of the physical frame are tinged with the peculiarities of these [the intellectual thoughts]." In Chapter 9, "The Leech," Chillingworth's motives and techniques are explored. As a scientific investigator, he cold-heartedly and intellectually pursues his lab specimen. Hawthorne says, "Few secrets can escape an investigator, who has opportunity and license to undertake such a quest, and skill to follow it up."
When Chillingworth begins his investigation, he does so as a scientist. Hawthorne writes, "He had begun an investigation, as he imagined, with the severe and equal integrity of a judge, desirous only of truth, even as if the question involved no more than the air-drawn lines and figures of a geometrical problem, instead of human passions, and wrongs inflicted on itself." Here the cold intellect of the publicly emerging nineteenth century scientist is used as a framework for Chillingworth's pursuit. This is what makes Chillingworth diabolical and, in Hawthorne's eyes, the greatest sinner. He violates Dimmesdale's heart and soul to see how he will react. Of human compassion, he has none. Eventually when Hester talks with him about whether Dimmesdale's debt has been paid, Chillingworth says that it would have been better had he died than endure seven years of vengeance.
Hawthorne also uses Hester to show what has happened to Chillingworth in isolating himself from humanity. In Chapter 14, she agrees with his description of what he used to be and counters with what he has become. He was once a thoughtful man, wanting little for himself. He was "kind, true, just, and of constant, if not warm affections." But now she tells him that he is a fiend, bent on Dimmesdale's destruction. She says, "You search his thoughts. You burrow and rankle in his heart! Your clutch is on his life, and you cause him to die daily a living death." In Dimmesdale, Chillingworth has a helpless victim, and he exercises his power over the minister with great enthusiasm. He enters Dimmesdale's heart "like a thief enters a chamber where a man lies only half asleep."
By Chapter 14, when Hester meets him in the forest, Chillingworth has a blackness in his visage and a red light showing out of his eyes, as if "the old man's soul were on fire, and kept on smoldering duskily within his breast." In seeking vengeance, he has taken on the devil's job. His obsession with revenge is what makes him — in Hawthorne's eyes — the worst sinner and, therefore, a pawn of the devil. It is appropriate that Hester meets him in the dark forest, a place the Puritans see as the abode of the Black Man. This man of science, so lacking in sentiment, is coldly and single-mindedly seeking what is only God's prerogative: vengeance.
Chillingworth has become such a fiend that his very existence depends on Dimmesdale. When he knowingly smiles to Hester at the Election Day ceremony, he is acknowledging that he, too, will be on that ship bound for Europe, the faithful companion of the minister. It is their fate to be together. When Dimmesdale surprises the physician and climbs the scaffold to confess, Chillingworth knows the minister is about to escape him. His mental torture of the minister is his only reason for living; when his object is beyond reach, Chillingworth does, indeed cease to exist.
In the Conclusion, we discover that Chillingworth "positively withered up, shrivelled away." Obsession, vengeance, and hatred consumed him, but, despite all this, he leaves his fortune to Pearl, a child of love and passion, the living symbol and personification of the scarlet letter. Perhaps this act can, to some degree, redeem the person whose sin was the blackest.