Hester Prynne and Arthur Dimmsdale, both have conflicts with society and their inner selves. While they can both be the protagonists, Hester Prynne is the protagonist of The Scarlet Letter, not Arthur Dimmsdale. .
In the first scaffold scene, Hester Prynne is described as having "figure of perfect elegance," and "beauty that shone out and made a halo of the misfortune in which she was enveloped." During the seven years after her sin, her beauty and warmth is gone and her hair is hidden under her cap all buried beneath the scarlet letter. After Hester removes the letter her beauty is back and it symbolizes her removing the harsh Puritan morals. Hester begins to perform charitable deeds like when she went to visit the dying governor. Eventually the town acknowledges that the A is for "Able." At the end, Hester lives on as the sin made her grow stronger.
Arthur Dimmsdale and Hester Prynne both have similar conflicts in the story. They have both sinned in a town with intolerance for sinners. However, Hester is the protagonist as she is able to find inner strength to help her overcome situations like when Pearl was going to be taken from her and the interviews that tried to find out who Pearl's father is. Dimmsdale did not have the inner strength to admit his sin. In fact, in the forest Dimmsdale admits he does not have the strength to go deep into the forest and free himself from the Puritans. Hester has to encourage him and even decides to join him as he revealed his sin. .
Hester Prynne is the protagonist in The Scarlet Letter. She is a survivor and her inner strength not only helps her overcome her sin but she helps Arthur Dimmsdale overcome his conflict with God and the Puritan society.