Topsy is like Simon Legree in only one way: she’s one of the most famous characters in Uncle Tom’s Cabin, but she appears in the novel relatively briefly. Still, the four characters from the book who have had a long afterlife in popular culture are Tom, Eva, Legree, and Topsy, so she’s more important than you’d guess from the few pages devoted to her.
Topsy is a mischievous, clever little girl who hasn’t been raised with any moral or intellectual instruction. In fact, she’s been raised in complete subjugation, beaten and whipped with any instrument that comes to hand by her heartless masters at a "low restaurant" that Augustine St. Clare passes on a regular basis (20.20).
Eventually, St. Clare’s conscience gets the better of him, and he buys Topsy from this restaurant to save her from mistreatment. But what St. Clare does with her is unfair in its own way – he gives her to Miss Ophelia as a gift, to train and instruct. Although St. Clare pities Topsy, he also treats her like an animal: he describes her as a "funny specimen" and whistles to her the way "a man would to call the attention of a dog" (20.7).
For her part, Topsy seems completely perverse and corrupted at first. She has "an odd mixture of shrewdness and cunning" and "something odd and goblin-like about her appearance" (20.5). She steals, lies, disobeys, and lazes about. No punishment has any effect on her, because she’s used to beatings – and also used to being told that she is wicked. She tells Ophelia, "I’s wicked, – I is. I’s mighty wicked, any how. I can’t help it" (20.100). This is what she’s been trained to believe by her previous masters: that, as a "nigger," she is inherently bad. And, sadly, she does believe it.
Ophelia is shocked and bewildered by Topsy, and the reader begins to realize why St. Clare put the two of them together. Although Ophelia can be high and mighty with the St. Clares when she’s telling them everything they’re doing wrong as slave owners, she can hardly bear to touch or interact with black people herself. She later admits this distaste when she watches Eva interact with Topsy. Ophelia can take physical care of Topsy, she can teach Topsy to make beds or say her catechism, but she’s still a racist: she doesn’t want to touch the girl.
All of Ophelia’s efforts with Topsy fail, and finally she’s ready to wash her hands of the girl, to have her whipped or even sell her on. Topsy is redeemed, not by Ophelia’s stiff-upper-lip rules and systems, but by Eva’s simple affection. Instead of threatening her with physical punishment, Eva simply hugs Topsy and says, "Poor child, I love you!" (25.48). Once Topsy realizes that she can be loved, and that someone believes in her, she begins the process of reform. Stowe tells us, with unusual realism, that:
Topsy did not become at once a saint; but the life and death of Eva did work a marked change in her. The callous indifference was gone; there was now sensibility, hope, desire, and the striving for good – a strife irregular, interrupted, suspended oft, but yet renewed again. (28.27)
Topsy’s conversion – both to Christianity and to good conduct – is Stowe’s way of demonstrating that dishonesty and crassness among slaves are largely the result of their mistreatment and abuse.
Nineteenth century slave owners often pointed to the "depraved" nature of their slaves as an excuse for continuing slavery, but Stowe won’t let them get away with this obvious chicken-and-egg ploy. The more masters abuse slaves, the worse the slaves become – and then the masters claim they can’t free the slaves because they’re wicked. Stowe shows us that whites must learn to love blacks as their Christian brothers and sisters if they want to bring out the best in them. Thus, Topsy also functions as a contrast to the obedient, saintly Uncle Tom, who seems too submissive and well behaved to be real, given the evils of slavery.