Person with competence to conduct an audit.

 Source: ASIS, ISO 9001 2000

Merriam-Webster Online Dictionary
auditor (noun)
a person authorized to examine and verify accounts
one who hears or listens , especially one who is a member of an - audience
a person who a course of study - audits
a person who hears (as a court case) in the capacity of judge
An auditor is an independent professional who examines and verifies the accuracy of financial records. The auditor's job is to provide an objective opinion on the financial statements of an organization. Auditors are responsible for examining a company's financial records and ensuring that they are accurate and in compliance with applicable laws and regulations.