Ralph is, of course, a central character in Lord of the Flies. He has many recognisable leadership qualities but does not yet have enough life experience or maturity to best use these qualities.His natural leadership most probably stems from his background - his father is a naval officer.
Piggy is almost like Ralph's alter-ego and without Piggy, Ralph would not be able to lead the boys at all. While Ralph has the abilities, he needs Piggy to guide him and direct him. Refer to the e-notes guides and navigate to the characters' page where you will find all the characters and you will understand the link between Ralph and Piggy. As it says in the character analysis:
He is the first to see the conch shell buried in the sand, though it is significant that it is Piggy who points out how it can be used as a signaling device.
Ralph is well-liked and wants to build a mini civilization on the island but his overall inability to lead effectively does contribute to this novel's theme and the boys complete descent into savagery. Even Ralph, himself, will not escape the inevitable.
Ralph's position as the elected leader and obvious choice will gradually decline whlie Jack's rises. Most of the boys, except Piggy, will leave Ralph in favour of Jack's 'tribe.' It is inconceivable for Ralph at first that the boys would give in to base instincts. However, like Simon, Ralph does come to understand taht savagery exists within them all. He works very hard not to be overwhelmed by the so-called 'thrill' of barbarism.
When Ralph hunts a boar for the first time, he does feel the exhilaration of the kill. When he attends the feast, he is further swept along and even participates in the killing of Simon.
As Ralph has not completely descended into savagery, he is plunged into despair by his actions but this experience also gives him the strength of character so that by the end of the novel he can defend himself against Jack's tribe by using the very stick that has come to represent the baseness and lost innocence of the boys - he casts the head to the ground.
His ultimate rescue also adds a burden to him as he now understands that lost innocence can never be recaptured.