North Korea has been viewed as the world's most reclusive, repressive, and isolated country for the last 70 years. However, contrary to its undeveloped image, since the late 2000s, several governments, mainly the U.S. and South Korea, as well as global private cybersecurity companies, have attributed some of the massive and complicated cyberattacks to the North Korean regime. Even, since 2014, the U.S. Intelligence Community's annual report, Worldwide Threat Assessment of the U.S. Intelligence Community, has stated that North Korea is one of the four primary nation-state actors in cyberspace who threaten the national security of the United States and its allies, along with Russia, China, and Iran. This paradox prompts the central question of this dissertation: why and how did North Korea become a world-class cyber-threat actor? This dissertation is composed of three independent, but thematically-linked empirical studies, replying to the central question. The first study (chapter 2) seeks to bridge the gap between North Korea's undeveloped image and cyber reality. It contends that contrary to its image as a backward country, North Korea has sufficient IT infrastructure and human capital to conduct hostile cyberoperations against the outside world in order to attain its national goals. The second study (chapter 3) is an empirical analysis of North Korea's cyber strategy. It argues that North Korea's cyber-proxy-warfare strategy enables its cyber-warriors to accomplish aggressive cyber-missions while North Korean hackers keep a distance from their state sponsor, North Korea. The last study (Chapter 4) seeks to understand the influence of North Korea's cyber uncertainty on regional and world security dynamics. It illustrates that through the North Korea case, the impact of cyber buildup can be seen as the same as that of conventional military buildup. When combined, these three studies provide insight into the central question of this dissertation about why and how North Korea became a world-class cyber-threat actor. The Kim dictator family has understood the importance and impact of developing cybercapacity for their survival in security and military areas. North Korea has started to conduct massive and complicated cyberoperations through a proxy-warfare strategy which enables the state to deny its responsibility for those operations. Sufficient IT human capital from state-led intensive education systems is at the core of North Korea0́9s aggressive cyberoperations; this, in turn, threatens the national security of other countries and changes regional security dynamics.