Though we know a great deal about Ralph's appearance, his abilities and even his charisma that helps the boys to elect him chief, there are very few pieces of information about his former life that come out.
The things we learn about his previous life come mainly in one paragraph. He tells Piggy that he could already swim well when he was five, that it was his father who taught him to swim, and that his father was a commander in the Navy. Ralph is confident that as soon as his dad gets leave, he will come find the island and rescue the boys.
The reader also learns that Ralph's father was there when he got on the plane at the airport.
Outside of that, the only information we get about Ralph in the first chapter is the description of his appearance, the beginning of his chiefdom and the conflict with Jack that will grow throughout the novel.