Robert, Mary Finch's brother, takes possession of Isabel and Ruth after his sister's death. In a lot of ways, he's like Madam Lockton—both see themselves as superior to their slaves and desire to get their grubby hands on a rich relative's money. For Madam Lockton, that person is Lady Seymour, while Robert's sister "wasn't even cold on her deathbed before when he helped himself to the coins in her strongbox" (1.8). He's also so inflexible on his views of slavery that he doesn't even believe Isabel when she says she can read and threatens to "beat [her] for lying" (2.16).
Still, without his inflexibility on the matter of Isabel's alleged freedom, we wouldn't get the rest of the story. Or two additional novels starring Isabel and Curzon. So really, he's the guy who makes all this go down, and—though we hate to say it—we wouldn't be doing this without him.