what is statutory auditor?

Answer 1

I thought they're auditors who perform statutory audits. In most countries, some companies are exempt from audit while some companies must be audited by external auditors as required by statutes. The latter audits are known as statutory audits since they are mandated by law. The auditors are thus the statutory auditors.
Among the companies which are exempt from audit by law, some would still choose to be audited, for their own reasons, e.g. the bank wants the audited accounts, the shareholders want to make sure the a/cs are in order, etc. But such audits are not statutory.

Answer 2

It's an official in Japanese Corporations: Statutory auditors are elected by shareholders and hold a position in the hierarchy alongside the board of directors. They do several things, initiate derivative suits, attend board meetings(monitor directors), audit financial reports and oversee the auditing performed by outside accounting firms.