Gamemaster
Compared to standard tabletop games (and to games meant to be played online), this online chat format changes the balance of duties for a gamemaster quite a lot. Descriptions require more preparation, even when using cut-and-paste; acting and voice skills can not be used to get the personality of NPCs and monsters across, making background music as a playing aid more useful. The GM is likely to need copies of player-character records, not being able to look at the originals as in a normal face-to-face game.  The format also forces the issue (particularly when players do not all know each other) of whether to leave all rolling of dice to the GM, or to trust all players to honestly give the results of their rolls (the honor system may be strained when rolling well is a very good thing).