Master of Life and Death - Robert Silverberg

When Roy Walton becomes the new director of the UN division of population control, after the director is assassinated, he becomes the most hated man in the world. Being Director involved him in not only population control, but a terra-forming project on Venus, and negotiations with aliens. Not only that, but some people were trying to kill him. To stay alive, he had to become The Master of Life and Death. Summary by Dale Grothman.