Who are Product Owners and what do they do?

What does a product owner do?
According to the Scrum Guide, a Product Owner orders the work for a complex problem into a Product Backlog. (Ref. Scrum Guide 2020. Page 3)
The Product Owner ensures that Scrum team members are prepared to discuss the most important Product Backlog items and how they map to the Product Goal.
This is just the tip of an iceberg, they do lot more than this, I am trying to keep it simple.
What is Product Owner’s accountability?
The Product Owner is accountable for maximizing the value of the product resulting from the work of the Scrum Team. How this is done may vary widely across organizations, Scrum Teams, and individuals. (Ref. Scrum Guide 2020. Page 5)
The Product Owner is also accountable for effective Product Backlog management, which includes:
● Developing and explicitly communicating the Product Goal.
● Creating and clearly communicating Product Backlog items.
● Ordering Product Backlog items; and,
● Ensuring that the Product Backlog is transparent, visible, and understood. (Ref. Scrum Guide 2020. Page 6)
Product Owners are accountable for lot of things, yet they can delegate their share of work to other people.
Do you know who represents the customer: The product owner represents the customer and guides the team as they deliver the product. The Product Owner proposes how the product could increase its value and utility in the current Sprint.
The product demo is an opportunity for the Scrum Team to demonstrate the product to the customer and it is driven by product owner.
The Product Owner may represent the needs of many stakeholders in the Product Backlog. Those wanting to change the Product Backlog can do so by trying to convince the Product Owner. (Ref. Scrum Guide 2020. Page 6)
Who has the authority the cancel the Sprint?
A Sprint could be cancelled if the Sprint Goal becomes obsolete. Only the Product Owner has the authority to cancel the Sprint. (Ref. Scrum Guide 2020. Page 8)
Before cancelling the Sprint, Scrum team can renegotiate the scope with the Product Owner.
Did you know:

The Product Owner is one person, not a committee.
How to run a successful team?
Scrum team is not complete without Product Owner and Scrum Master and for the Product Owners to succeed, the entire organization must respect their decisions. These decisions are visible in the content and ordering of the Product Backlog, and through the inspectable Increment at the Sprint Review. (Ref. Scrum Guide 2020. Page 8)
Did you know:

The Scrum Master coaches the Product Owner on best practices of Agile and Scrum.
This is a part of Decoding Scrum Guide 2020 series.
Article 2 — How does Scrum help to achieve continual improvement?
Article 3 — How to make Scrum Successful?
Article 4 — Why everyone despise scrum theory?
Article 5 — Daily Stand-ups are waste of time.
Article 6 — Let’s get rid of Scrum Master.
Article 7 — Who are Product Owners and what do they do?
Article 8 — Who are Developers? What are their Accountabilities?
Article 9 — The notorious Scrum Team.
Article 10 — Why do we need Sprint Planning?
Article 11 — Is your Scrum Team failing in its commitment.