Authors often give their characters names that reflect their personalities, and you might think that Douglass is doing that too. Two of the worst overseers he works for are named Mr. Gore and Mr. Severe, and he even jokes about how "Mr. Severe was rightly named." Once you start looking for them, you'll find quite a few examples. Mr. Covey, for example, is an extremely covetous (greedy) person, and one of the best masters Douglass works for is named Mr. Freeland. But it turns out that these were all the actual names of the real people Douglass was talking about. Sometimes truth is more interesting than fiction!
A lot of writers operate under the principle of "showing, not telling." Douglass is not really that kind of author. When he describes the people he's known, he usually just gives it to us straight, telling us who they were and what they were all about. For example, he tells us that Mrs. Auld was a kind woman when he first met her, but owning a slave made her cruel and robbed her of her compassion. When he describes Mr. Covey, he tells us from the start that he was a cruel and deceptive man without a trace of human kindness.
Every time he gets a new owner or overseer, Douglass makes a point of noting what kind of master he is. Mr. Severe and Mr. Gore are cruel and vicious overseers, while Mr. Hopkins is more fair. When Douglass goes to work for Mr. Auld in Baltimore, he is given a lot of privileges and is allowed to learn a trade. But there really is no way to be a good slave owner, as Douglass discovers with Mrs. Auld. She starts out a good person, but the very fact of owning a slave corrupts her to the point of becoming even more cruel than her husband. And it's when Douglass is working for Mr. Freeland – his best master – that he realizes that no master is as good as being your own master. Instead of working for Mr. Freeland, he says, he'd rather live in a free land.