He calls himself César Torres, he is not really a human, he is a stand-in who stole the identity of the real César Torres.
His main goal was to kill as many humans as possible, his tactic is to emotionally destroy them by gaining their trust while feeding on fear.
He is incapable of feeling physical pain and is obsessed with feeling it, he wants to understand pain.
Despite everything, he is capable of feeling emotions and even empathy, to the point of becoming obsessively attached to Mark.