Which character shows conformity in Lord of The Flies and what are some quotes that prove it?

Virtually all of the boys on the island show conformity at one time or another in the story. We see this in the first chapter, when all of the boys clamor for a leader.
Eventually, Ralph is chosen to be chief. Meanwhile, Jack Merridew is chosen as the head of the hunter group (which comprises the members of Jack's school choir). Both Ralph and Jack display conformity from the very beginning of the story. The difference between the two, however, is of what each chooses to conform.
Ralph believes that right conduct is imperative to the preservation of a civilized society. To enable right conduct, certain rules must be followed by everyone. Ralph prizes these rules and conventions, and this can be seen in how he interacts with the boys under his charge. Meanwhile, Jack believes that "might makes right." He believes that a true leader is characterized by his strength of will and his ability to intimidate his followers. In chapter 2, Jack plunges his knife into a tree trunk for emphasis: he'll kill a pig the next time he sees one. Jack's actions have the effect intended. All the boys immediately settle down. So, Jack believes in rules, but he demonstrates little compassion for those he leads.
Essentially, Jack and Ralph conform to differing concepts of leadership. In chapter 2, we see Ralph imposing rules about orderly conduct. Jack is thrilled that Ralph is insisting on "rules," but his joy is actually inspired by the prospect of punishing boys who refuse to conform. In chapter 4, Jack reveals his macabre fascination with blood and violence. He describes slitting the pig's throat and the "lashings of blood" that flowed from the dying animal.
In turn, Jack and Ralph's differing leadership styles end up splintering the group. The boys from Jack's choir largely opt to follow Jack and his dictates. Meanwhile, boys such as Piggy and the twins (Sam and Eric) choose to throw in their lot with Ralph, who always believes in doing the principled thing. In chapter 11, the four boys lament Jack's style of leadership, which Piggy terms irresponsible.
Piggy is another example of a conformist in the story. Largely unpopular, Piggy chooses to follow Ralph. In the story, Piggy is willing to obey Ralph because he believes that the latter exemplifies all that is best in a leader. In chapter 11, Ralph resorts to the only negotiation tactic he knows: dress for conflict and present one's case logically and calmly to one's enemy. Ralph is wholly preoccupied with the facade of civilization, even when the situation has descended into chaos. He admonishes the small group to dress like boys, not "savages," so that they can approach Jack in a manner he deems proper.
Yet, Ralph's concept of civilized negotiation falls by the wayside during the meeting with Jack. When Jack attacks Ralph with a spear, the latter is forced to engage in violence in order to defend himself. It is Piggy who tries to save the day. He implores the boys to think about whether it would be better "to have rules and agree, or to hunt and kill." Piggy tries to appeal to the boys' better natures, but to no avail.

"I got this to say. You're acting like a crowd of kids." The booing rose and died again as Piggy lifted the white, magic shell. "Which is better—to be a pack of painted Indians like you are, or to be sensible like Ralph is?" A great clamor rose among the savages. Piggy shouted again. "Which is better—to have rules and agree, or to hunt and kill?" Again the clamor and again—"Zup!" Ralph shouted against the noise. "Which is better, law and rescue, or hunting and breaking things up?"

In the end, Piggy dies; his death is caused by Roger, a loyal follower of Jack. Piggy dies in a gruesome manner, suggesting that conformity to the rules of civility is useless when the framework for civilization has been lost.
So, in the story, the main characters differ in how they portray conformity. For boys such as Ralph and Piggy, conformity to tried and true principles is portrayed as a means of deliverance from savagery. Meanwhile, boys such as Jack and Roger portray conformity to conventional rules as a useless paradigm for survival in dire circumstances.