Dr. Jekyll is a good guy who plays by the rules. He reads books about religion, he does charity work, and although he throws dinner parties for his bachelor friends. The focus of Dr. Jekyll’s bachelor parties is science, religion, and literature. But Dr. Jekyll does have one nasty little secret: he longs to be evil and give way to many unspecified "appetites." His name perhaps provides a clue: "Je" in French means "I," while "kyll" = kill. The question is, what or whom does he kill? Himself? His appetites? His good side? His evil side?
After contemplating and analyzing these appetites of his, Dr. Jekyll decides that all men are both good and evil, and the clear thing to do is to try separating these two opposing facets. Dr. Jekyll – who is apparently a scientist as well as a doctor – experiments with a variety of potions with this goal in mind. He eventually mixes a potion that, when consumed, turns him into Mr. Hyde. Instead of a "large, well-made, smooth-faced man of fifty […] with every mark of capacity and kindness," he morphs into another person entirely – an evil person.
It’s important to note that Dr. Jekyll has a conscience. He knows what he’s doing is bad. He even admits that as Dr. Jekyll, he sometimes works to fix the harm that he caused as Mr. Hyde. But eventually, he just can’t help himself. He has to participate in a world of pleasure no matter what it costs him.