Who is Hyacinthus?

Prince Hyacinth went running to recover the discus. His bare legs were a blur, his dark-blond curly hair coming loose from its knot. Running west into the wind, the young man might have gotten the sun in his eyes, so he didn't see that he was closing dangerously on the flying weapon. When the discus hit the ground, it rebounded off a rock. The sharp edge slammed Hyacinth right in the face. As the young man collapsed in the dust, a shout of Horror went up from the watchers.