Details about GMs before GMA are sketchy at best. GMs started as Forum RPs set around Sonic, not the MFW. Troophead was the one who coined the term "Group Mission". Aside from a certain historical reference, these very early GMs don't have an actual practical use for the MFW based RPs and GMs.
The very first GM that was actually set in the MFW (though the setting was not called that way at the time--TBlood coined the term "Mobius Forum World" and its abbreviation "MFW" during GMA--was during Zifei Wu's days; Zifei is the founder of Sonic HQ).
The very first main Villain for the MFW was Pyroclad. Apparently, Pyroclad was pretty much the first big time flamer the Mobius Forum knew. (Writer's note: I think he was also the very first hacker to strike the Forum, but that could also be his bosom buddy; Maron). It was no wonder he was used as the villain in the very first MFW based GM. Pyroclad pretty much wanted to burn down the MFW, but was eventually defeated by the forumers led by Zifei and Troophead and a host of a few others.
It is unclear how many GMs followed after the one against Pyroclad. At some point Zifei quit his position at the SHQ, and WB ascended in the position of Webmaster. It was under WB that the MFW started to shape up in the world we pretty much know today with Sega City, Rubber Chickens and other notorious elements.
It was also around THAT time that Evil WB made his appearance in the GMs. The last GM just prior to GMA featured Evil WB as the main villain, wanting to topple the Moderators (back then there were no Admins). To that end he had constructed some sort of Space Station and had kidnapped the original WB. The Forumers eventually managed to rescue WB and defeated EWB.
The next GM, though definitely not the best, was destined to reshape the face of the MFW.
GMA - Group Mission Apocalypse
GMS - Group Mission Sailorness