Ralph R. Swick posted on usenet to announce the first version of what we now know as X11, or just X (as version 11 seems to be the final cut):
The X Window System, Version 11 Release 1 is now available. This release represents a major redesign and enhancement of X and signals it’s graduation from the research community into the product engineering and development community. The X Window System version 11 is intended to be able to support virtually all known instances of raster display hardware and reasonable future hardware, including hardware supporting deep frame buffers, multiple colormaps and various levels of hardware graphics assist.
Whereas the design and implementation of the first 10 versions of X were primarily the work of three individuals, Robert Scheifler of the M.I.T. Laboratory for Computer Science and Jim Gettys of DigitalEquipment Corporation and Ron Newman of M.I.T., both working at M.I.T. Project Athena, X version 11 is the result of the efforts of literally dozens of individuals at almost as many locations and organizations.
I was not an X user until SPARCStations came out, I think, in pizza box form factor, which seems to have been 1992. I do recall a relatively major update of X in the SunOS days - perhaps a site had to build its own X then? I don’t recall what the version might have been.
I vaguely remember a short demo in C - might have been an IOCCC entry - which showed an X client could be written in just a few lines. Conventionally, it takes a lot of boilerplate (I think.)
I’ve used twm often enough, and used to use xbiff, and xload (or something similar) and of course xclock. I do recall CDE, and Motif. And I had a monochrome (1 bit deep) X Terminal for quite a while. We used to use NCD X Terminals, earlier Tektronix, IIRC.
(Image from Wikipedia: