The comparison of the characters of Richard III and Macbeth is a critical consideration of long standing. The practice dates back to the eighteenth century, in fact, and a bit of thought on the matter makes it easy to see why. They are both monarchs who achieve their positions through treachery and murder, whose crimes become increasingly vicious until they eventually reach the level of infanticide, who lose all manner of human connection, who become conscience-wracked and are eventually defeated in battle by nemeses who personify the attributes that they've left aside in their pursuit of power. There's more, including the fact that both were renowned for their feats in battle before their turn to villainy, and that the historical counterparts to the characters each have quite a number of vigorous defenders who have argued that Shakespeare's depictions of them were unfair, and were meant to flatter his own monarchs (Elizabeth I in the case of Richard III, and James I in the case of Macbeth). But the really surprising thing in all of this, after all of the parallels that can be drawn, is that the characters have very little in common in psychological, philosophical or dramatic ways. And to paraphrase several commentators, a dramatist of lesser skill would have made them interchangeable.