"One project, one Product Owner." Just like Highlander, there can be only one. However, stories are generally told from a specific viewpoint, and well-written stories often reference beneficiaries and collaborators.
Viewpoints, Beneficiaries, and Collaborators
When writing a user story, the generally accepted format involves starting with a viewpoint that defines the end-user or primary beneficiary of a feature. For example:
As a wealthy "one-percenter"
I want lower estate taxes
so that my children's inheritance is taxed more lightly than other income.
In this example, the critical viewpoint for the user story is that of the wealthy one-percenter. Sometimes the viewpoint character is someone the team will work with directly, but sometimes others act as proxies or spokesmen for the viewpoint.
The potential benefits of a story are not limited to the viewpoint character. In this example, the children also benefit from the feature even though the story isn't told from their point of view. They are beneficiaries of the user story.
As written, the user story also implies a number of other collaborators: attorneys, probate courts, tax advisors, and so on. These are people that may need to be consulted or actively engaged in order for the team to complete the story properly.
In my experience, collaborators (as opposed to the story's viewpoint or beneficiaries) are often implied by the story rather than explicitly called out. This may be a good thing that provides needed flexibility in story execution, or it may be a bad thing that makes the story's tasks less transparent to the project. Your mileage in this regard may vary widely.