The M'Naghten Rule is a legal standard used to determine whether a defendant can be held responsible for a crime due to mental illness. Established in 1843, it states that a person is not criminally responsible if, at the time of the act, they were unable to understand the nature of their actions or distinguish right from wrong due to a severe mental disorder. This rule is often applied in criminal cases where the defendant claims insanity as a defense. It emphasizes the importance of mental capacity in assessing culpability, ensuring that individuals who cannot comprehend their actions are treated differently under the law.