Henry Jekyll is a man who is proud of his upstanding reputation and position in the community, but he struggled with his darker side which presented him with temptations and behaviors that his good side was ashamed of and had difficulty dealing with. In an effort to discover more about the dual nature of man, Henry Jekyll begins experimenting and creates a potion and drinks it, willingly risking his life.
Dr. Jekyll believes that he has succeeded in separating the dual nature of man, the good from the evil. So when he sees Mr. Hyde, he is thrilled, even though Hyde is hideous looking and much smaller in stature.
With Hyde released, and Jekyll carefully hidden beneath, Mr. Hyde is set free to be wild and violent without consequences. His vicious nature released, Dr. Jekyll is able to indulge in his dark passions without shame or guilt. He is pleased with the arrangement, as Mr. Hyde, Jekyll is animalistic in nature, but he bears no responsibility as Dr. Jekyll.
"Jekyll has a mixed response to his alter ego. When he drinks the potion and transforms into Hyde he at first admits, "I felt younger, lighter, happier in body; within I was conscious of a heady recklessness, a current of disordered sensual images running like a millrace in my fancy ... an unknown but not an innocent freedom of the soul. I knew myself at the first breath of this new life, to be more wicked, tenfold more wicked, sold a slave to my original evil;"
Dr. Jekyll believes that he needs Mr. Hyde in order to live a good and pure life. He is able to absolve himself of temptations and desires, exercising them as Mr. Hyde so as Dr. Jekyll, his behavior is impecable, beyond reproach, he is civil, polite, upright and law abiding.