Stevenson presents Dr. Jekyll as a suitably complex character. On the face of it, he's a thoroughly decent man, the very epitome of Victorian respectability. His friends—of whom there are many— describe him as showing "every mark of capacity and kindness." Moreover, it's telling that he's further described as "smooth-faced" implying that the face he presents to the world is completely different from what lurks inside him.
Yet Dr. Jekyll has a dark side, which gradually takes him over, body and soul. Although his diabolical alter ego Mr. Hyde is a murderous psychopath, and the complete opposite of Jekyll in all respects, Hyde doesn't just emerge out of nowhere. Even when outwardly normal, there's still an air of mystery about Jekyll that puts us on our guard, no matter how "smooth-faced" he is. For one thing, he's an incredibly secretive man, especially in relation to his scientific experiments; he also pointedly refuses to divulge his connection with Hyde to Utterson.
For all his superficial charm and kindness, we suspect there's a lot more to Dr. Jekyll than meets the eye. His single-minded, almost obsessive commitment to science compromises his relationships with others. Indeed, his friendship with Lanyon is cut off due to Jekyll's alleged "scientific heresies."
Jekyll's foolish experiments with Hyde could be interpreted as a sign of selfishness on his part. In allowing himself to be taken over by Hyde, Jekyll's indulging a hidden desire for freedom, a desire to break free from the numerous moral and social constraints of Victorian England. It is only by being Hyde that Jekyll can experience the kind of freedom that, deep down, he wants more than anything else. This is what makes him such a compelling character, as well as a complex one.