I'd think first and formost you'd have to discuss their origins in tabletop RPG's.

Also there is discussing the various types of RPG's that exist, and the originals.

You had their original start (Or at least when they started gaining some steam) whith Richard Gariott's Ultima series, and how that insipred Hylude (I might have spelled that wrong), a game that kicked off the popularity of RPG's in Japan, who became massively influential in the Genre.

That would be a good area to start I guess.