The Silent Warrior

Thousands of years in the future, Earth is a desolate ruin. The first human ship to return in millennia discovers an abandoned wasteland inhabited only by a few degenerate or mutated human outcasts. But among them is a boy of immense native intelligence and determination who is captured, taken in, and educated, and disappears--to grow up to become the force behind a plan to make Earth flower again. He is, if not immortal, at least very long-lived, and he plans to build an independent power base