Jacob is full demon with speed and straingth is greater then Inuyasha and Sesshmaru. His parents are both dead because Sango the demon slayer killed them they was trying to protect their child. Jacob is on his own side which he later takes over Inuyasha's body. He has the ability to take over other human and demons bodys he hates Inuyasha his father was killed when he was 12 until he comes and tries to kill Inuyasha with a soul sword called the soul tessiga which is more powerful then Inuyasha and Sesshmaru's swords he wants to kill Inuyasha because he is blamed for killing his family he comes across turing into his demon form which is different then from Inuyasha and Sesshmaru's his body lights on fire which is now in fearting with Jacob. He promised to avenge his family with the help of Inuyasha he's in search of his mother.