Horus

The Emperor and Horus engaged one another in the throne room of the massive battle barge, a battle that was both physical and psychic in nature. Though the Emperor's psychic gifts and martial skills were unequalled, he found himself unwilling to summon his full strength against his beloved son. The Emperor suffered grievous wounds at Horus' hands, and after a score of thrusts, parries and counter-thrusts between the Emperor's Runesword and his own Lightning Claw, Horus sliced open the Emperor's chest armour, then opened his jugular and severed the tendons in his right wrist, disarming the Emperor. A psychic blast seared the flesh from the Emperor's face, destroying one of the Master of Mankind's eyes. After tearing the Emperor's right arm from its socket, Horus raised his father high over his head, and broke his back over his knee.