Who are these leaders?

Sarah, thy wife, shall bear thee a son and thou shall call him Isaac: and I will establish my covenant with him for everlasting covenant for his seed after him. And as for Ishmael, I have heard thee: behold, I have blessed him and will make him fruitful and will multiply him exceedingly, twelve leaders shall be beget, and I will make him a great nation.” (Turaat Genesis 17: 19-20)