What term describes a person whose criminal responsibility is in issue in a criminal action?

The term that accurately describes a person whose criminal responsibility is in issue in a criminal action is "actor." In legal terminology, an "actor" refers to an individual who is directly involved in the commission of a crime, essentially the person whose actions are under scrutiny in the case. This term underscores the role of the individual as the one who allegedly committed the criminal act being challenged in court.

The other choices do not accurately describe this person. The defendant is a broader term typically used to refer to a person being accused in a criminal case, which isn’t specific to the concept of criminal responsibility. The complainant is the person who brings forward the accusations, often the victim or a party who is alleging that a crime has occurred. A witness is someone who provides testimony about the events related to the crime, but they do not have the same level of direct involvement as the actor in question.