Secondary responsibilities of the Product Owner

The Product Owner is also responsible for

owning and the prioritisation of the product backlog.
creating a successful product roadmap that meets both the needs of the business stakeholders and the existing and targeted customers.
the user stories that form the product backlog but is not solely responsible for writing the user stories.
working closely with the agile team throughout the product life cycle by attending various ceremonies, e.g. Daily Stand-ups, Iteration (Sprint) Planning and the Retrospectives to give valuable and timely input.
promoting Agile principles and is responsible for constantly adjusting the product backlog in response to planned and unforeseen changes to constantly maximise business benefit.
owning, driving, and focusing the agile team on delivering business value.
ranks and prioritises user stories in preparation for the sprint planning activity and conveys a clear vision of what is required to be built.

Additional information, including working examples and templates are available in the Monetical knowledge base.