In Lord of the Flies, Jack represents the Id, or the unconscious, in his desire to be chief, to rule, and to implement his power with violence. When hunting, Jack finds himself unable to kill a pig because of the violence of it; however, his desire to be seen as leader by the other boys allows him to overcome this disgust by hiding his humanity behind a mask of mud and leaves:
Beside the pool his sinewy body held up a mask that drew their eyes and appalled them. He began to dance and his laughter became a bloodthirsty snarling. He capered toward Bill, and the mask was a thing on its own, behind which Jack hid, liberated from shame and self-consciousness.
(Golding, Lord of the Flies, gv.pl)
The mask, hiding his face, allows his Id to rule his Ego, and shows his true nature; without it, the other boys can see Jack, who is just like them. With the mask, however, he is something more, and feels capable of accomplishing more, but his inner nature creates unnecessary violence instead of leadership.