The regulator for public-sector recordkeeping. The Chief Archivist issues the mandatory standards under the Act and must authorise the disposal of public and protected records, unless another Act requires it.
The Chief Archivist's authority is what makes disposal defensible: public and protected records generally cannot be destroyed without it, and unauthorised disposal can trigger offences and remediation. That authority is usually exercised in practice through disposal authorities managed by your IM/RM function.
Disposal of public and protected records requires the Chief Archivist's authority unless another Act requires the disposal. In practice that authority is granted through approved disposal authorities and schedules rather than case by case.
IAR turns terms like this into working practice: assets classified against your disposal authority, stewarded by position, and ready to evidence.