1) main person in a business. 2) employer, the person hiring and directing employees (agents) to perform his/her/its business. it is particularly important to determine who is the principal since he/she/it is responsible for the acts of agents in the “scope of employment” under the doctrine of respondeat superior. 3) in criminal law, the main perpetrator (organizer and active committer) of a crime, as distinguished from an “accessory” who helps the principal in some fashion. the criminal principal is usually the person who originates the idea of committing the crime and/or directly carries it out, and is more likely to be charged with a higher degree of the crime, and receive a stiffer prison sentence. 4) chief, leading, highest.