Who is responsible for writing the RCA?

In most enterprises the problem manager or the incident commander is formally accountable for the RCA, and a senior engineer on the affected service actually writes it. In ITIL organisations the role sits with problem management; in SRE organisations it usually falls to the on-call engineer who led the incident, sometimes with a customer success manager chasing the customer-facing version. Accountability is often clear on paper and unclear in practice, which is why RCAs slip past the contractual window. The alternative is to make the RCA a delivered service: an outside team investigates and drafts, the internal owner reviews and signs, and a single party is answerable for the deadline.