optimus prime, superman, captain america, captain planet, the ideal leader, they are real in a platonic sense, and ideas are as real as flesh and blood. The ideal leader can be embodied to an extent by many leaders in many places throughout history. But it is rare for the real to match the ideal, for the imperfect to reach perfection. But it is not impossible for there to exist ideal leaders, and at most these symbolic representations would be but artistic representations of the embodiment of the ideal.
I do believe that people can live up to the ideal, and that the ideal can manifest physically. Myths may come to be built, but underneath the heroes, upon which legend is built, can be just as legendary as the legends they inspired.