Urusei Yatsura is usually considered the root, with Ranma being the one that defined its cliches going forward.

I'm sure there are ones that fit into the criteria, but nearly all the ones from the 90s onward draw inspiration from Rumiko Takahashi and her work. Shit nearly every "main girl" in most harem's are just Akane Tendo again.

Though I googled the question just to see if there was one I just had never heard of, and apparently Archie Comics is considered the original harem series and the one that inspired Japan on it. So that's a thing too.