Who is Nicolai Mikhailovich from The Mark of the Assassin: A Novel and what is their importance?

Born the bastard son of a Soviet Union KGB Chief, Nicolai was turned over to a mentor, Vladimir, and trained from childhood to become an assassin. At age 16, he was sent into the West to perform assassinations as instructed by the KGB. With the breakup of the Soviet Union, however, Nicolai was out of work. He became an independent contractor, using a fellow Russian as his "agent." He takes up residence in a small French village, taking the name Jean Delaroche, and operates from this location.