Although Shakespeare presents Richard III as being physically deformed, modern historians doubt whether this was true. Nevertheless, in the play, he is presented this way and it is intimated that his evil appearance hides a soul that is even more evil. The actions of the play bear this out. Richard III of the play is born evil. His mother even tells him that she has had no joy in him since the day he was born. He is conniving and ambtious and lets nothing stand in his way, not even innocent children if they are in line for the throne of England.

As the play progresses, Richard does seem to be ovecome by his own evil, in my view. The night before the battle where he is eventually killed, he cannot sleep, has nightmares and sees the ghosts of people he has killed. He even says:

''I have not that alacrity of spirit / Nor cheer of mind, that I was wont to have,"

There is an excellent character analysis of Richard III here on enotes that I suggest you read for further insight into your question.