Charley and Howard Wagner serve as the parameters within which Willy Loman must behave in order not to demonstrate that he is pretty much finished as a salesman, and broken as a man.
Charley is Willy Loman's neighbor. He is a practical man and, essentially, a good man. He is aware of Willy's impractical life philosophy of just living for the moment, to be liked, and to be popular. However, he has known Willy for so long that it does not bother him, in fact, it pleases him, to try and help Willy by giving him some money. He knows that, even though he offers Willy a job, Willy's pride would be too hurt to accept. Willy is so broken at this point that he would rather take money, instead of being actively giving up his empty fantasy of being a well-liked salesman. Hence, Charley is the voice that Willy needs to hear: He is reality, and he is convention. Willy is fantasy and superficiality.
On the other hand, Howard Wagner is the son of Willy's former boss. A symbol of nepotism in a corrupted society where the fittest survive, Willy is now the young man's employee. Far from the grandeur He expects as a salesman, Willy is reduced to begging for a new type of job in the company- only to be told that he is no longer even needed. Humiliated , Willy returns home literally to die. He has been given the last clue as to how far his dreams are. In all, Charley is Willy's reality, and Howard brings reality back to Willy in a cruel manner.