Microsoft Write (which supported RTF) was included in Windows 1.0 - https://en.wikipedia.org/wiki/Microsoft_Write

For Win95, the new included-in-the-box email client required a text editor which supported multiple fonts, colours, font styles, et al. But Microsoft Write code was not written to be modular and cross-platform (much of the Win95 email client code would also run on the Macintosh, for Mac OS System 7.x).

So the RichEdit windows control was created.

Wordpad.exe is a thin wrapper around the RichEdit control, like Notepad.exe is a thin wrapper around the text edit control.