No, this isn't the global chat of your favorite game, and no the answer doesn't start with World and end with Warcraft. According to veteran designer (and current Star Wars: The Old Republic producer) Rich Vogel, Meridian 59 was the first MMO, as there were "a lot of firsts with that game, for sure. It was really the first 3D visual of a virtual world, if you want to say that."
In a new interview at Gamasutra, Vogel talks about everything from M59, to Star Wars Galaxies, to Ultima Online (and how the PvP minority managed to ruin it for virtual world enthusiasts everywhere). "Frankly when you give people a simulator and the ability to do anything in the world you have to have limits, you have to have constraints that they understand," Vogel explains. UO's free-form PvP, coupled with the thieving mechanic and the ability to manipulate the game world to your advantage, was a recipe for griefing that caught the game's developers completely off guard.
"It went through eight or nine iterations before we kind of found a balance of what really worked and what didn't. But it was certainly an experience and many people talk about their experiences in UO. The experience there, no one's ever been able to duplicate today," Vogel says.