Auditor
Also called independent accountant, certifying accountant.
The independent accounting firm that audits a company's annual financial statements and gives an opinion on them.
The auditor's report appears with the audited financial statements in the 10-K. Source 1
A change of auditor is reported on an 8-K under Item 4.01, including whether there were disagreements with the former auditor. Source 2 Source 3