There aren't very many characters in the Scarlet Letter so you have no excuse for not getting them all down. If you can't recall all of them, your teacher will know you didn't read it.
Hester Prynne - Considered by some "the first true heroine of American fiction," Hester Prynne withstands harsh looks, an unforgiving society, and a really, really, wimpy lover. She is forced to wear a scarlet 'A' as punishment for committing adultery. Her strength along with her Christian charity turns Hester from someone to be scorned into someone who is admired.
Arthur Dimmesdale - Dimmesdale, Hester's partner in crime, is outwardly angelic but inwardly corrupt. He is a foil to Hester: where she is strong - he is weak; she is shamed publicly - he is honored publicly; she is honest - he is not. He fears what men think more than what God thinks. He forgoes the peace that only confession and repentance could bring in order to seek public accolades. His moral weakness manifests itself through physical illness.
Roger Chillingworth - Hester's husband shows up after a long absence and sees his wife being put to public shame in the town square, not exactly the happiest reunion for either. He attempts to persuade Hester to give him the name of her lover, but she refuses. He vows to discover it himself. He extracts a promise from Hester not to reveal his identity. He spends his time exacting revenge on Dimmesdale through the use of herbs, hypnosis, and medicines. His inward evil manifests itself through physical deformities.
Pearl - Hester's daughter, perhaps the first single parent child in American Literature, does what many children do, temper the behavior of their parent. Pearl's existence forces Hester to bridle her passions in order to keep Pearl. Pearl is portrayed as a witch, a fairy, and a sprite. Hester dresses her to look like a living embodiment of the scarlet letter and a reminder of her past sins.
Governor Bellingham - The governor at the time of Hester's transgression, Bellingham, at one point, wishes to remove Pearl from Hester, but is swayed by Dimmesdale (who has been covertly threatened by Hester immediately prior to speaking (you'll have to read the actual passage in chapter 9 where she all but says you'd better make sure I keep my child or else!)).
Mistress Hibbins - The governor's sister is a witch. Everyone seems to know it but him. She recognizes Dimmesdale for who he is.
The Narrator - Most people don't read the introduction to the book, The Custom House. It's incredibly wordy. It is in the introduction that we meet the narrator who comes across an account of Hester Prynne more than 200 years after the incident and writes a fictional account of her life.
A Short Analysis
Hawthorne brilliantly develops the novel's two main characters, Hester and Dimmesdale. They are human. They have weaknesses and they both overcome weakness through suffering--the former outwardly, the latter inwardly. Hester is made strong through shame whereas Dimmesdale is made weak through shame. To automatically consider Hester a moral superior overlooks the probability that if not for the pregnancy, her sin would have never been discovered and she would have lived as Dimmesdale, outwardly pious and inwardly untamed.
Hester's willingness to keep her lover's identity a secret is offset by her willingness to keep Chillingworth's identity a secret. Notwithstanding, Dimmesdale allowing Hester to withstand public humiliation alone is a far greater betrayal, one for which he pays a grave price.