Roger is a mystery from the beginning, and seems to have a dark character.
It seems that while some of the boys know each other, especially the choir, no one knows Roger or where he came from.
There was a slight, furtive boy whom no one knew, who kept to himself with an inner intensity of avoidance and secrecy. He muttered that his name was Roger and was silent again. (ch 1)
Roger is actually very important. When you watch him closely, you will notice that he is the impetus for a lot of the action. First of all, he is usually quiet but when he speaks up he makes things happen. He is the one who first calls for a vote. He also makes suggestions about the fire, and tells everyone that he has been watching the water and there are no ships.
Roger seems to have a dark side. Roger and Maurice destroy the littleuns play area for no reason. Roger is the instigator. At this point we are given a physical description of him that reinforces the darkness in his personality.
He was not noticeably darker than when he had dropped in, but the shock of black hair, down his nape and low on his forehead, seemed to suit his gloomy face and made what had seemed at first an unsociable remoteness into something forbidding. (ch 4)
Roger starts throwing stones, and although he throws to miss it is only the influence of civilization, which happens to be slowly leaving him.
Roger goes with Ralph and Jack to inspect the mountain. Since Roger is “uncommunicative by nature,” he does not offer an opinion on the beast. He also stabs the pig much more aggressively and repeatedly than necessary. In the pig dance, Roger plays the pig.