[vintagedave]

> it's simple enough that, if not for him, someone else would've came up with it

The thing is, no-one else did. It's very easy to point to something being simple and obvious decades after it has become omnipresent.

Plus, someone has to be first. And he was first.

The core part of this is not the underline, or possibly even doing it asynchronously though on desktop software at the time that was more rare, but the squiggly underline. I strongly doubt squiggles are a choice anyone else may have made. A solid underline, school-teacher-style, maybe.