Stanley is a waiter and bartender at Frank's Chop House, which is the restaurant to which Biff and Happy invite Willy to dinner in hopes to celebrate the good news that they hope come after Biff's sought-after meeting with Bill Oliver.
Stanley is the quintessential bartender-listener-conversationalist who is able to grasp the gist of the different situations that he witnesses, and still maintain his objectivity. He is quite familiar with Happy Loman and seems to be in awe of Happy's conversational skills with the ladies, namely, Miss Forsythe and then Letta. He waits on Willy and Biff with diligence and respect, as well.
Stanley is also the witness of the dysfunctional dynamics of the Lomans. While the Lomans try to show to the world an image of themselves that does not exist, Stanley witnesses in their actions the shallowness of Happy, the traumatic personality of Biff, and the mental instability of Willy. When the men engage in an argument, Biff leaves angrily while Happy drags the ladies with him going after Biff.
Willy, in the middle of a hallucinatory, flashback is left at his own mercy back at the restaurant. Stanley is who comes to the rescue to look out for Willy. This is when Willy tries to give Stanley money that Stanley puts back on Willy's pocket. Then Willy asks Stanley whether he knows of a place that sells seeds. Stanley, without any judgment, directs Willy to a hardware store, and watches him go, making sure that Willy is alright.
Moreover, Stanley also ensures that Willy is left with a little bit of dignity, as he scolds a fellow waiter who had been staring at the entire situation with the Lomans. Stanley tells him
Well, watta you looking at!?
Therefore, Stanley represents the good Samaritan and also epitomizes the good American citizen. He is what every good citizen should be: a good man who listens, does not judge, does his job, and just looks out for others. He is the only man in the restaurant who gives Willy respect, and care. He even looks out for Willy's dignity. We could say that, when measured against all the Lomans, Stanley is, literally, the bigger person among them all.