He's a ten year old boy who has gone from kind and compassionate to cruel and cunning, wishing to destroy as much of the world as he could without believing in anything anymore. Law suffered a mental breakdown and, according to Doflamingo, came to be known for being very cruel and nihilistic. Law became nihilistic and omnicidal, wishing to destroy as much of the world as he could without believing in anything anymore. He is an angry child learning to love.