Dr. Phoenix is the main antagonist of The Dragon's Tooth who kidnaps Cyrus and Antigone's older brother Daniel Smith. He appears throughout the series and is rivaled in evil only by his enemy Radu Bey.
Dr. Phoenix is a bloodthirsty being with hidden motives. In some cases it can be believed that he is after ultimate power, immortality, or even purely science though none of that has been stated as truth. It can be assumed that he wishes to remake the world in his own image.