A threat actor, also known as a malicious actor or bad actor, is either a person or a group of people that take part in an action that is intended to cause harm to the cyber realm including computers, devices, systems, or networks. Threat actors exploit vulnerabilities in computer systems, networks, and software to perpetuate a variety of cyberattacks, including phishing, ransomware, and malware attacks. The term is typically used to describe individuals or groups that perform malicious acts against a person or an organization of any type or size. Threat actors have different educational backgrounds, skills, and resources, and they engage in cyber-related offenses to exploit open vulnerabilities and disrupt operations. The background of threat actors helps dictate who they target, how they attack, and what information they seek. There are different types of threat actors, including cybercriminals, nation-state actors, ideologues, thrill seekers/trolls, insiders, and competitors. These threat actors all have distinct motivations, techniques, targets, and uses of stolen data. Threat actors can be classified into different categories based on their motives and objectives. Threat actors can possess a multitude of skills, tools, resources, and techniques to carry out malicious activities, and these capabilities can vary widely depending on the motivations, expertise, and resources of the threat actor.