He ensures that the Team delivers value to the business, always considering the stakeholders’ needs. Sometimes he gets screwed by people outside the project, but a good P.O. makes his name and can even turn enemies and traitors into allies.
Each one has their unique style, but they are all cross-functional, having the skills to do what needs to be done in order to deliver. The really great team members will strike down with furious anger those who would attempt to poison and destroy the quality of the work. But beware: cocky ones eventually get caught with their pants down and meet unfortunate ends.
He facilitates Scrum by removing impediments. He solves problems. He knows the rules. Time and resources may look tight, but if you do what he says, when he says it, it should be plenty.
People who enable the project and for whom it will produce the agreed-upon benefits. When they get too involved with members of the team, bad things happen to everyone.