When William Golding's Lord of the Flies was published in 1955 in New York, The New York Times Book Review declared it an allegory, and since then many critics have concurred with this judgment. Certainly, Golding's novel is in response to the 1857 British work, "The Coral Island" by R. M. Ballantyne in which a group of Victorian boys are shipwrecked on a tropical island, but the boys conquer the external evil of the cannibals on the island.
As an allegorical response to the question of man's struggle against evil, the characters of "Lord of the Flies" are far less complicated that those of typical novels. Therefore, it is a difficult task to pigeon-hole these characters as "flat" or "round" since allegorical characters represent abstract qualities rather than act as individual personages in a regular narrative. Piggy, for instance, represents the adult world of society with its rationality and order and rules. His glasses are symbolic of rational thought and common sense; when they are broken, the order of the group is damaged. And, when they are stolen from Piggy by Jack, chaos wins; all rationality is gone. It is then that Roger, who represents unbridled sadism and evil, throws Piggy against the rocks, those atavistic vestiges of time that smash his brain.
Is Piggy a round or flat character? He is more than a character, for he represents the abstract qualities of reason and order. That Piggy stands for reason is evident on the final page as Ralph weeps for
the end of innocence, the darkness of man's heart, and the fall through the air of the true, wise, friend called Piggy.
Similarly, Roger is neither a round or flat character as he represents the sadism in man held only in check by the punishment of society. His description in Chapter 4 verifies this abstraction: He is dark, gloomy, with black hair that runs down the nape of his neck and low on his forehead. When little Henry plays seaside, Roger stoops for a stone, "that token of preposterous time," bouncing it near Henry. Only the conditioning of "a civilisation that knew nothing of him and was in ruins" stays Roger's arm. Later, once the conditioning of civilisation wears off, Roger--innate evil--emerges in the forest and dashes Piggy against the "tokens of preposterous time" and kills him.
Little Simon, inarticulate and quiet, represents the spiritual side of man; the intuition. He alone recognises the inherent evil in the boys, for as he is faced by the Lord of the Flies, he hears it say, "You knew, didn't you?" Intuitively, Simon identifies Beelezebub, knowing that the evil of men is internal, rather than an external beast.
Jack represents leadership by intimidation. At first, he maintains some order as leader of the boys' choir, but his fear causes him to act tough. To hide his humiliation when he tries to discredit Ralph, Jack leads an uprising and becomes chief of the hunters. Outside the realm of Piggy and Ralph, reason and order, he makes rules that are enforced with physical punishment--a job for the sadistic Roger.
On the other hand, Ralph represents leadership by government and order and common sense. However, as hardships and tension increase, Ralph loses hold of his leadership and his common sense. His struggle with Jack indicates the conflict between order and savagery.
While Ralph and Jack are allegorical, there can be an argument for them as rounded characters, for they seem to have more than one salient characteristic unlike all the others. For instance, Ralph, like a real boy, has flaws. He ridicules Piggy at times, he grows angry, he enjoys a pig hunt, succumbing to his more savage nature; he becomes frustrated when the others will not listen, he recognizes that Piggy can think better than he--regretfully, in fact. Ralph is not static in his nature; he tries to learn and change. Likewise, Jack makes efforts at first to be part of the entire group by saying he will be in charge of certain tasks. But, his pride makes him desire to be leader, and when he cannot win leadership in an orderly fashion, he usurps it as he steals the fire.
To me, of the major characters, Jack is the flattest. I guess I'd say Ralph and maybe Simon are rounded.
To me, Jack has very little in the way of redeeming qualities. He is power hungry and he is selfish. He does not seem to have any sort of inclination to try to be better.
By contrast, Ralph tries to do the right thing. He tries to keep order and do what is needed to get the boys rescued. But he's not just a flat "good guy." He can be a jerk, as he is with Piggy a lot of the time.
Out of the characters in the book Lord of the Flies I have to agree that Jack lacks depth. From the beginning interaction at the first assembly when he made the statement that he should be the leader, the reader could identify that he would later create some degree of conflict. His emersion into the savage comes quickly with little to no remorse. He is very atypical of the school yard bully and evil is easily represented by his behavior.
Simon is the most round character to me. He is a far deeper study than the other boys. Through Simon the reader is able to see beyond the pretense of the beast and begins to identify that the beast exists within the boys. He feeds the littluns, studies the boar's head, contemplates the idea of the beast, identifies and frees the pilot, and is savagely killed when mistaken as the beast, and yet, he is the least likely of the older boys to be a beast. He is a representation of a Christ-like figure which sends the reader looking for deeper meaning within the story.