Who is Comte de Saint-Germain from The Magician and what is their importance?

The Comte de Saint-Germain is one of history's mysterious figures. He reportedly was an alchemist and possibly was involved in the occult. Germain is also known to have been a great composer. In this novel, Germain continues to pursue music and has become something of a famous techno musician. He aids Flamel and the twins when they arrive in Paris, even teaching Sophie the magic of fire.