Hyde, as his name indicates, represents the fleshy (sexual) aspect of man which the Victorians felt the need to "hide" — as Utterson once punned on his name: "Well, if he is Mr. Hyde, I will be Mr. Seek."
Hyde actually comes to represent the embodiment of pure evil merely for the sake of evil. When he is first extracted and in our first encounter with him, he is seen running over a young girl, simply trampling on her. He does not do this out of spite — or intentionally; it is simply an amoral act. He does make reparations. But even in this first encounter, he raises a fear, an antagonism, and a deep loathing in other people. The reaction of others to him is one of horror, partly because while looking at him, others feel a deep desire to strike out at him and kill him. In other words, his mere physical appearance brings out the very worst evil in other people.
Since Hyde represents the purely evil in man (or in Dr. Jekyll), he is, therefore, symbolically represented as being much smaller than Dr. Jekyll — Jekyll's clothes are far too large for him — and Hyde is also many years younger than Jekyll, symbolically suggesting that the evil side of Jekyll did not develop until years after he was born.
