One might question the extent to which Dr. Jekyll and Mr. Hyde are in fact a single character. Until the end of the novel, the two personas seem nothing alike—the well-liked, respectable doctor and the hideous, depraved Hyde are almost opposite in type and personality. Stevenson uses this marked contrast to make his point: every human being contains opposite forces within him or her, an alter ego that hides behind one's polite facade. Correspondingly, to understand fully the significance of either Jekyll or Hyde, we must ultimately consider the two as constituting one single character. Indeed, taken alone, neither is a very interesting personality; it is the nature of their interrelationship that gives the novel its power.

Read about another morally conflicted protagonist in Shakespeare’s Richard III.

Despite the seeming diametric opposition between Dr. Jekyll and Mr. Hyde, their relationship in fact involves a complicated dynamic. While it is true that Jekyll largely appears as moral and decent, engaging in charity work and enjoying a reputation as a courteous and genial man, he in fact never fully embodies virtue in the way that Hyde embodies evil. Although Jekyll undertakes his experiments with the intent of purifying his good side from his bad and vice versa, he ends up separating the bad alone, while leaving his former self, his Jekyll-self, as mixed as before. Jekyll succeeds in liberating his darker side, freeing it from the bonds of conscience, yet as Jekyll he never liberates himself from this darkness.

Jekyll's partial success in his endeavors warrants much analysis. Jekyll himself ascribes his lopsided results to his state of mind when first taking the potion. He says that he was motivated by dark urges such as ambition and pride when he first drank the liquid and that these allowed for the emergence of Hyde. He seems to imply that, had he entered the experiment with pure motives, an angelic being would have emerged. However, one must consider the subsequent events in the novel before acquitting Jekyll of any blame. For, once released, Hyde gradually comes to dominate both personas, until Jekyll takes Hyde’s shape more often than his own. Indeed, by the very end of the novel, Jekyll himself no longer exists and only Hyde remains. Hyde seems to possess a force more powerful than Jekyll originally believed. The fact that Hyde, rather than some beatific creature, emerged from Jekyll’s experiments seems more than a chance event, subject to an arbitrary state of mind. Rather, Jekyll’s drinking of the potion seems almost to have afforded Hyde the opportunity to assert himself. It is as if Hyde, but no comparable virtuous essence, was lying in wait.

This dominance of Hyde—first as a latent force within Jekyll, then as a tyrannical external force subverting Jekyll—holds various implications for our understanding of human nature. We begin to wonder whether any aspect of human nature in fact stands as a counter to an individual’s Hyde-like side. We may recall that Hyde is described as resembling a “troglodyte,” or a primitive creature; perhaps Hyde is actually the original, authentic nature of man, which has been repressed but not destroyed by the accumulated weight of civilization, conscience, and societal norms. Perhaps man doesn’t have two natures but rather a single, primitive, amoral one that remains just barely constrained by the bonds of civilization. Moreover, the novel suggests that once those bonds are broken, it becomes impossible to reestablish them; the genie cannot be put back into the bottle, and eventually Hyde will permanently replace Jekyll—as he finally does. Even in Victorian England—which considered itself the height of Western civilization—Stevenson suggests that the dark, instinctual side of man remains strong enough to devour anyone who, like Jekyll, proves foolish enough to unleash it.