PLATO is notable for being the origin of the of the computer role playing game. The history of early CRPGs is murky, because PLATO was intended for educational use and games programmers had to work in secret to avoid the administrators deleting their work, but it's possible that the first ever CRPG was the Reginald Rutherford's 1975 game "The Dungeon" (a.k.a. "pedit5" after its inconspicuous lesson name). The Dungeon was probably earlier than the lost game "m199h" that was previously thought to be first. These early CRPGs are all influenced by Dungeons and Dragons, which was first published in 1974.

The Dungeon is still playable today. The CRPG Addict blog has details:

http://crpgaddict.blogspot.com/2019/01/revisiting-dungeon-19...

And more information about lost games:

http://crpgaddict.blogspot.com/2021/06/brief-everything-we-k...