How is Ralph described in he beginning of story? Why might he make good leader?

Ralph is described as a fair boy with athletic movements. He is juxtaposed with Piggy, the first boy he meets, who is fat and has asthma. Ralph is the first boy to blow the conch so the boys see him as a leader. Golding also adds that:

"He was old enough, twelve years and a few months, to have lost the prominent tummy of childhood and not yet old enough for adolescence to have made him awkward. You could see now that he might make a boxer, as far as width and heaviness of shoulders went, but there was a mildness about his mouth and eyes that proclaimed no devil."