I believe the mainframe version was first.
There is a version baked into the os/400 operating system (i series).
Then unix/windows Db2 came last, if memory serves.
I came here to say that if you want to understand Oracle's value, think IBM with less history.
IBM is a bit more nuanced. My wife grew up in an IBM town and a lot of her family and her friends’ families used to work there in the 70s and 80s. People, especially the engineers, used to take pride in their work there.