There are multiple definitions - click on the translation that matches your context.

Beschwerdeführer

Substantiv

partial

complainant

Comparative law notes

Germany

Our recommended translation in the event that the context is more generalized and is not part of a formal judicial or administrative process.

Definitions of complainant

English

a person who brings a civil action in court or who makes a criminal accusation that leads to a criminal prosecution

The complainant filed suit seeking damages for breach of contract.