This is an old question with different answers. As any other people, following the reasoning of Spanish philosopher Ortega, a leader is a mix of himself and his experiences, then, the solution is easy: or we use genetic engineering or the leader must be born. Later, the leader must learn to be a leader.
Today many people try to make leaders with incorrect DNA. They use marketing to manufacture a leader, but marketing will never produce strength, intelligence or any other capabilities that a leader could need in a certain period of time.
This one is an incorrect vision of the marketing activity. Perhaps, we can sell someone who does not exist, but this does not imply that we have made the product.
For instance, intelligence is not contagious, although we put always a person near an intelligent one, he will never become cleverer.
A good marketing vision will focus on improving the experiences of a potential leader, as we can expand a product with associated services, but it should not focus on telling lies about his DNA, or his competence.