Achilles "The Greatest Warrior"

We know that Achilles was almost like a God in a sense, because he was born to take lives and had a very little chance to be killed. He knew he was the greatest warrior ever born, but he also knew that his life would end if he stood in Troy to fight for his honor and glory. Although he redeemed himself after returning Hector's body to the king of Troy Priam, why did he have to humiliate Hector by dragging his body throughout the battlefield with his chariot in the presence of the Trojan royalty?