Glengarry Glen Ross
Speaking of beating Levene in the end, say hello to John Williamson—the antagonist of this play.
In a touch of structural genius, Mamet puts protagonist and antagonist literally across the table from each other in the first scene. He shows us what the protagonist needs (good leads) and the obstacle standing in the protagonist's way (the antagonist controls who gets the leads). It's simple and elegant:
LEVENE: I need your help.
WILLIAMSON: I can't do it, Shelly. (1.1.180-181)
The brilliance of this conflict is that it goes away for quite a while. Levene and Williamson start the show, and then we don't see either of them again until Act 2. When they finally come together again, everything leads to Williamson's victory over Levene.
Feeling good about his major sale, Levene no longer feels as though he needs Williamson' s help:
LEVENE: You are a shithead, Williamson. (2.1.980)
Unfortunately for Levene, he needs Williamson's help again all too quickly. When Williamson figures out Levene is the crook, he has the ability to let him off. What good is an antagonist who gets out of the protagonist's way, though? They might be a decent human being, but they're probably not pulling their weight when it comes to plot advancement. Worry not, though—Williamson is a tried and true antagonist, and in the end he gets Levene to confess, to turn Moss in, and sends him into the cops. "Why?" Levine asks. "Because I don't like you," Williamson replies. Boom—that's some nice antagonism right there.