Who is the antagonist in "The Passing of Grandison"? Explain why the character is the antagonist. Use evidence from the story to support your answer.

The antagonist of the story is Colonel Owens, the father of Dick Owens. He attempts to thwart his son's goals and is ultimately unsuccessful.
While Dick's actions in the story aren't exactly noble, he is still working to do something good—give a man his freedom. He's only doing this to impress the woman he loves; ultimately, he ends up with her for other reasons. His father, however, attempts to stop Dick from helping a slave go free. His character is one that has a positive attitude toward slavery. This is shown when he hesitates to let the slave of Dick's choice—Tom—travel north with him.
Charles Chestnutt writes:

"I don't think it safe to take Tom up North," he declared, with promptness and decision. "He's a good enough boy, but too smart to trust among those low-down abolitionists. I strongly suspect him of having learned to read, though I can't imagine how. I saw him with a newspaper the other day, and while he pretended to be looking at a woodcut, I'm almost sure he was reading the paper. I think it by no means safe to take him."

He does this in several ways:
Colonel Owens chooses a slave he believes to be satisfied with his life in the South.
He offers Grandison, the slave, the right to marry the woman he loves when he returns home.
He makes Grandison promise that he won't run away when Grandison and Dick go on their trip together.
Chestnutt writes:

"What's the matter with Grandison?" suggested the colonel. "He's handy enough, and I reckon we can trust him. He's too fond of good eating, to risk losing his regular meals; besides, he's sweet on your mother's maid, Betty, and I've promised to let 'em get married before long. I'll have Grandison up, and we'll talk to him."

When Grandison comes home after Dick stages his escape by having him kidnapped, it seems that Colonel Owens is vindicated. He gets his comeuppance in the end when Grandison escapes with multiple other slaves in tow.