Good exposition and referencing the origins of Scrum back in the 1990s helps show the progression. I wrote about this topic back in 2011 in a number of articles. Here's but one of them.

http://onproductmanagement.org/2011/05/the-scrum-title-product-owner-must-die/

The Product Owner was intended as a "role", not a job title, but even Sutherland's writing at the time were unclear and a mishmash of different contents blended into one.

I had hoped. that by now (20 years later) this would have been cleared up, but unfortunately there's still a lot of confusion to be addressed.