VERY first was probably a tie between Diablo and Quake
Battle.net was a brand new concept back then, and Quake was always a pain to find good games on, you had to use a third party program like Gamespy, the posted game data like IP addresses, because everything was just TCP/IP back then (or IPX/LAN, if you were with a bunch of friends). The lag was horrendous because everyone was using dialup.
Online gaming kind of sucked back then.
Another major early Online game I played was a small MUD called "Darkover". There was never more then about 50 people playing the game (and I mean that there were 50 active people, rarely was there more then 20-30 on at any given time, usually there was 5-15), but we managed to have 3 major guilds, who actually competed with one another (I was in all 3 at some points of my playing), and for a while, we had RP Immortal Worship.
I was Dirkin, a gnome mage who remorted Faerie, and I worshipped Vash, the god of poetry and rhyme.
I don't even think that game runs anymore.. but I played it for 8 years.
mtk2a post=9.73305.792160 said:
Warcraft 2 on a LAN.
Then, Diablo 1 on battle.net
If we're counting LAN/IPX, then Warcraft 2 for me as well. I was going by Online meaning on the internet