Who is Ruby from Johnny Got His Gun and what is their importance?

Ruby is the Shale City girl who is every boy's first sexual conquest. Ruby, is a big, fat, Italian sixth or seventh grader, when Joe Bonham's turn comes as a seventh and ninth grader. All the boys begin with Ruby because she does not embarrass them. They laugh about her and soon grow ashamed of her. By tenth grade, they have nothing to do with her and she disappears, to their relief.