What the dickens
Where had you this pretty weathercock?
I cannot tell what the dickens his name is my husband had
him of. What do you call your knight's name, sirrah?
Sir John Falstaff.
Ford:The Merry Wives Of Windsor Act 3, scene 2, 18–23
Sir John Falstaff!
"What the dickens!" is an oath referring, not to Charles, but to Satan. "Dickens" probably derives from a common English surname, or from "Dickin," the diminutive of "Dick." The reason it was substituted euphemistically for "devil" in the exclamation "What the devil!" probably has little to do with the behavior of some naughty Dickens, though. As with that other devilish substitute "deuce" ("What the deuce!"), the reason almost certainly lies in the sound and in the comic effect of the substitution itself. Many similar examples in Renaissance or modern English may be found—such as "marry" for "Mary" and "gosh" for "God."
Master Ford stumbles here into the middle of an elaborate plot, concocted by his wife and Mrs. Page, to foil the lecherous advances of Sir John Falstaff. Ford sincerely believes that Falstaff will succeed in seducing his wife—if he hasn't already—and is therefore rather nervous about signs of collusion between Falstaff and his wife's comrade, Mrs. Page. That Falstaff's page Robin has become part of the Page household gives Master Ford some pause.