Petitioner – in many legal systems this term refers to the legal figure of a person who submits a petition, signed by many others, towards an official institution in order to start legal process related to a legal question in dispute, which is considered with the petition to be of importance for huge group within the society. For example, this could be the applicant to the court. Synonyms are
“appellant”, “claimant” and ‘inquirer”.

See also “petition”.