Assessing the risk posed by Advanced Cyber Threats (APTs) is challenging without understanding the methods and tactics adversaries use to attack an organisation. The MITRE ATT&CK provides information on the motivation, capabilities, interests and tactics, techniques and procedures (TTPs) used by threat actors. In this paper, we leverage these characteristics of threat actors to support informed cyber risk characterisation and assessment. In particular, we utilise the MITRE repository of known adversarial TTPs along with attack graphs to determine the attack probability as well as the likelihood of success of an attack. We further identify attack paths with the highest likelihood of success considering the techniques and procedures of a threat actor. The assessment is supported by a case study of a health care organisation to identify the level of risk against two adversary groups– Lazarus and menuPass.