Constantine XI Palaiologos, was killed in 1453 when Constantinople fell to the Turks. Constantine led a last, fatal charge, and was later recognised only by his imperial purple boots.
It was said that an angel turned the Emperor to marble and placed him in a cave near the Golden Gate, to one day be brought back to life and restore the Roman Empire. He is a national hero in Greece for his defiant stand against the Ottomans, and is considered a saint by some.
There is a parallel with Friedrich Barbarossa, who in German legend sleeps in a mountain until the Holy Roman Empire is restored.