The protagonist is Death's godson. He became the a world-renowned doctor. "It was not long before the young man had become the most famous physician in the whole world."
The antagonist is Death himself. He took the protagonist as his godson, and gave him the gift of being the most famous physician in the world. He treats the rich and the poor equally. "I am Death, who makes everyone equal."
Death's godson betrayed him. "You have betrayed me. I will overlook it this time because you are my godson, but if you do it again, it will cost you your neck, for I will take you yourself away with me."