What is a person called who requests an investigation or action is taken, often the victim of a crime?

A person who requests an investigation or action and is often the victim of a crime is known as a complainant. This term specifically refers to someone who files a complaint with the authorities or law enforcement, seeking some form of recourse or resolution to a grievance, particularly in the context of a crime. Complainants provide essential information that serves as the foundation for an investigation and may be directly involved in the legal process, either as victims or individuals who can provide critical testimony regarding the events in question.

The term emphasizes the proactive stance of the individual in seeking assistance or justice regarding the situation they are facing. In legal terminology, the complainant plays a pivotal role in the initiation of legal proceedings, as their report or complaint is what triggers action from law enforcement or judicial systems, making this designation distinctly relevant in both criminal and civil matters.