In William Golding's Lord of the Flies, when Ralph first proposes the idea of electing a leader in Chapter 1, he actually uses the term chief: "Seems to me we ought to have a chief to decide things." The term chief is echoed throughout the passage, even when Jack insists he should be chief, until Ralph is finally, reluctantly, elected. Since a chief is a "ruler of a tribe or clan," it may often work as a perfect synonym for your paper considering that throughout the book, the boys begin acting more and more like what some might consider to be barbarian tribal members (Random House Dictionary).
A synonym similar to chief is head, and head imagery actually appears frequently throughout Lord of Flies, so it too may be a perfect synonym in your paper for leader. One classic example of head imagery appearing in the book is the boar's head covered in flies that Simon becomes mesmerized by in Chapter 8, after Jack's tribe had killed the boar they had been hunting. The head covered in flies represents the Lord of the Flies, which is another name for Satan. Also, the fact that it is a head can symbolize the deterioration of leadership among the boys.