In Scrum, everything starts with product owners and the product backlog.
The product owner role has a very specific meaning in Scrum.
It is the person accountable for maximizing the value of the product or service assigned to the team.
Is product owner same as a product manager?
In Scrum, there is no project manager. I repeat, there is NO PROJECT MANAGER.
So a product owner cannot be and should not be a project manager. The developers/creators act, as group, as project manager. Scrum is about self management. If you implement a project manager role in your team, you are not doing Scrum. It may work out, but it is not Scrum, and that might be a problem if team members expect something else.
The product owner role is not a committee. It is one person. And that person is obsessed with both what customers want and what developers / creators produce. This duality is why a product owner is different from a product manager. The role is actually a technical role more than a marketing role.
Still, understand that a product owner must put customers first. The focus is clearly on creating the maximum value for their and for the business. But this is done from a technical perspective in the sense of making sure it happens in the product.
Can a product manager also be the product owner?
Yes, absolutely, as long as you make sure to switch hats. A product manager has other responsibilities, and the role is firmly in marketing and sales, which is a different focus. Product owner is in production and delivery.
The instrument a product owner uses to fulfill its role is the product backlog.
"A product backlog is a list of the new features, changes to existing features, bug fixes, infrastructure changes or other activities that a team may deliver in order to achieve a specific outcome." - Scrum Alliance
Therefore, you should expect that everything the team creates comes from the product backlog.
The only person allowed to manage the product backlog is the product owner. Sure, it is possible to delegate and, in some ways, work as a group managing the backlog. This is strictly at the product owner's discretion. Because nothing in Scrum gives the right to anybody else to amend, add or remove anything from the product backlog without the direct consent from the product owner.
The product owner also has the power to terminate a Sprint. This is an awesome power and it should be avoided, but this is possible.
All this power is counter balanced by the fact that developers / creators, are the only ones allowed to decide how they convert product backlog into actual increment. The product owner decides what, and the developers/creators decide how.
Also, time estimates and the details of a sprint are not decided or even directed by the product owner. This is often misunderstood. This is why there is this confusion, in teams new to Scrum, that product owners are project managers for the team. As mentioned earlier, they are not.
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