There is a lot of symbolism in Cloud Atlas, but the one that stands out to me is St. George and the Dragon. It is not only portrayed in statues of St. George in parts of the movie, but in the character Old Georgie in Zachry’s visions/hallucinations.
There is much more to the movie, but one major thread, where the Tom Hanks character must overcome his own internal struggles throughout different lives, to me is the main theme trying to come across in the movie. He must not defeat an external dragon, but himself, his own evilness. I think this is portrayed in two parts, one where the statue of St. George is shattered, and the other where Zachary must defeat Old Georgie, which is of course himself. The Dragon is St. George himself.
This is an old motif, portrayed in the stars. The constellations Orion and Draco are St. George and the dragon, known by different names throughout the ages and cultures, but nonetheless the same. These two constellations seesaw back and forth throughout the 25,920 year cycle of the Precession of the Equinoxes. It is an age-old battle that we must all go through for spiritual growth. Each one of us is Old Georgie, and must go through many lifetimes in order to perfect ourselves, and overcome our own lower chakras, giving rise to the upper, spiritual chakras.