Meet the Cast

Della - a devoted woman.

The narrator describes Della as the loving, heartwarming, soft and a little bit hysterical protagonist of the story. Della's "mistress of the home", because of a poverty they live in. She only lives for one thing person: Jim, her husband. She's spent a lot of the time thinking of a Christmas for him:
"She had been saving every penny she could for months, with this result. Twenty dollars a week doesn't go far. Expenses had been greater than she had calculated. They always are. Only $1.87 to buy a present for Jim. Her Jim. Many a happy hour she had spent planning for something nice for him."
We can notice from the citation, that Della throws all energy, all herself into her love to Jim. She's been saving for months just to collect money for a Christmas present. She has even tolerated the humiliation of taking pennies at stores.
Jim deserves the best, that is why Della's so tries to find him the perfect present: "Something fine and rare and sterling – something just a little bit near to being worthy of the honor of being owned by Jim".
Della is ready to go to any length to achieve this goal, and as a result sells her one prized possession – her hair. Although she at first was sad about cutting her hear off, really it didn't affect her that much. She has to get Jim a present: "I had my hair cut off and sold because I couldn't have lived through Christmas without giving you a present. It'll grow out again – you won't mind, will you? I just had to do it".
Actually, the only thing that Della is worried about losing her hair is if Jim likes it or not. She's concerned he won't find her beautiful anymore. She doesn't think of herself at all. And this is her feature of character that insipres and at the same time strickes me. That's her sacrifying devotion.

Jim -a loving man.

Jim's the only breadwinner of the Dillingham family, and he works a lot, but his salary is low. And not long ago it went worse: before he used to make $30 a week he's now getting $20. He and Della are struggling just to pay for their small flat. So if Jim happens in the story to look  a little exhausted, serious, and probably underweight, there's a reason for it.
"He looked thin and very serious. Poor fellow, he was only twenty-two--and to be burdened with a family! He needed a new overcoat and he was without gloves."
Only his love for Della keeps Jim standing. His description proves that he is just as devoted to Della as she is to him. That's why Jim gives up his most precious possession to find a perfect gift for his lover. "Don't make any mistake, Dell," he said, "about me. I don't think there's anything in the way of a haircut or a shave or a shampoo that could make me like my girl any less."
We may wonder...Why does Jim love Della so much? Perhaps partly because she loves him so much.
We also have noticed that Della is also a little jumpy. Jim's definitely the more levelheaded one in the relationship. While she reacts to his present with shrieks and wails, he just reacts to hers by rolling onto the couch and smiling.

Madame Sofronie - a sharp contrast.

Madame Sofronie is the owner of a hair shop, which sells "hair goods of all kinds". She is depicted as "large," "white," and "chilly". Her manner is direct, she is not impressed by Della's gorgeous hair at all, and casually offers to buy it for $20.
Madame Sofronie's attitude creates a sharp contrast to Della and Jim. For both of them, Della's hair is a treasure – and Della's sale of it amounts to an enormous sacrifice. None of this matters to Madame Sofronie, for whom it's just another profit. We can claim she represents "the cold, uncaring world" which is outside the home of love Della and Jim have built for themselves.