The Puppeteer. Nathan K, #11

Nathan K - he can hold two souls in his body. If he dies, he loses one yet lives on with the other. As long as he replenishes his second soul, he cannot be killed. Nathan K is immortal. FACING A MADMAN Years ago, Nathan had one encounter with Russo, the Puppeteer, and it nearly killed him. Permanently. But when he started his war against the Immortals, he knew someday he would have to go up against Russo again.
Meeting Deanna Altman, an ex-MI5 agent bent on vengeance for Russo's abuse of her sister, Nathan knew that day would come sooner than planned. Now, with the help of his constant companion and tech genius, Robin, the three have tracked Russo into South Korea. But finding the Puppeteer and taking him down are two very different things. Matters only get worse when a mysterious boy who might be able to give Russo more power, a secret sect of monks that trade their lives for a taste of immortality, and the North Koreans all get involved. Yet if they can survive, Nathan and his team will strike a major blow in his personal war.