Who are Shelly Levene and John Williamson?

David Mamet's play shows the author as a perfectionist. He orchestrates the dialogue like a composer, sometimes directing two characters to keep interrupting each other or to speak at once. Mamet seems to have chosen his characters' names with great care. Shelly's reminds the audience of the English Romantic poet Percy Shelley. This is appropriate because Shelly Levene has a vivid, though crooked, creative imagination and a sort of vernacular eloquence. By contrast, John Williamson could not possibly have a more commonplace name. It sounds like an unoriginal alias. His name makes him seem anonymous, invisible, ineffectual, stereotypical, a colorless factotum--but he surprises Shelly and the audience.
Mamet planned his play to be full of surprises at the end. John Williamson, who has taken scathing verbal abuse from Shelly Levene and even more from Richard Roma, suddenly reveals his intelligence, suppressed emotions, and moral strength when he makes Shelly confess to being the one who broke into the office, faked a generalized burglary, and stole those precious Glen Garry leads. Naturally everyone in the audience has been thinking that George Aaronow is the guilty party, just as everyone has been thinking that John Williamson is a total wimp, and just as everyone has been pleased to hear that Shelly has broken his bad streak by selling eight units of Mountain View to Bruce and Harriett Nyborg for $82,000. Williamson not only demoralizes Shelly by deducing that he burglarized the office and by forcing him to implicate Dave Moss, but he destroys Shelly completely by telling him that the Nyborgs are "nuts." Williamson says, "The people are insane. They just like talking to salesmen." At the end, Shelly Levene is a broken man.