Peggotty is David's old nurse and his mother's housekeeper. Her primary characteristic, so far as we can see (besides the red, rough cheeks David keeps teasing her for) is her loyalty. Even though Mrs. Copperfield frequently yells at Peggotty, Peggotty never deserts her. Even though the Murdstones try to freeze Peggotty out of the house, she promises she "won't leave [Mrs. Copperfield]" (4.129).
After Mrs. Copperfield's death, Peggotty moves to Yarmouth to marry Mr. Barkis. Despite his miserly ways, she looks after him with great devotion. Once Mr. Barkis has died, Peggotty moves to London to act as a servant for David and Miss Betsey again. She immediately begins keeping house for David and then for Miss Betsey as though it is what she was born to do.
In other words, in this strongly class-segmented society, Peggotty seems to be a model of working-class womanhood. She loves looking after people, and she knows her place (a major point of contrast with the ill-fated Emily). Peggotty doesn't have much of a character of her own – though she's a lot more perceptive about the Murdstones than Mrs. Copperfield manages to be.
Peggotty's main role in the novel is to introduce David to a range of good, poor folk with whom he can hobnob, in contrast to his more prosperous days with Miss Betsey and in London. Peggotty is so loyal and self-sacrificing that she almost seems like a stereotype: the ideal of what a well-placed gentleman like David would want his servants to be. (For more on Peggotty's role in the novel, check out our section on the Crocodile Book in "Symbols, Imagery, Allegory.")