Chillingworth is Hester's husband who arrives in Boston after being shipwrecked on an island with Indians. He assumes the persona of Dr. Chillingworth, not wanting anyone to know he is Hester's husband. His success stems from the fact that some people in Dimmesdale's church want him to help Dimmesdale. They are concerned about Dimmesdale because his health is declining. They, of course, don't know that Dimmesdale is suffering from guilt, an ailment which can't be cured by any medicines. By attaching himself to Dimmesdale, Chillingworth secures a place in society since Dimmesdale is so greatly respected by his parishioners, and they want him to to help Dimmesdale.
Chillingworth is actually Hester's husband. He has assumed this identity to mask this fact. He does not want people to know who is is, as he has a plan to find out the identity of Hester's lover. Chillingworth has been held captive with the Indians and has only just come to town.
Chillingworth is now Dimmesdale's constant companion and doctor. The church elders are concerned with Dimmesdale and beg him to become his patient. Chillingworth is using leeches, and this is symbolic of the leeching he does on Dimmesdale's psyche. He is probing him psychological more that physically. At first, he did not know that Dimmesdale was Hester's lover, just that he had a dark secret. Chillingworth is constantly pushing to know the secret. Townspeople are taking his changing appearance into account as well, as he is growing darker and uglier. It is rumored he learned strange medical practices during his time with the Indians. Dimmesdale is not getting any better despite the constant care of Chillingworth.